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Document and Entity Information - USD ($) $ in Millions	12 Months Ended
Document and Entity Information - USD ($) $ in Millions	Dec. 31, 2018	Mar. 01, 2019	Jun. 29, 2018
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	FY
Trading Symbol	OCUL
Entity Registrant Name	Ocular Therapeutix, Inc.
Entity Central Index Key	0001393434
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		42,836,572
Entity Public Float			$ 224

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 54,062	$ 41,538
Accounts receivable	201	226
Inventory	217	122
Prepaid expenses and other current assets	1,713	1,453
Total current assets	56,193	43,339
Property and equipment, net	10,236	10,478
Restricted cash	6,614	1,614
Total assets	73,043	55,431
Current liabilities:
Accounts payable	2,965	3,571
Accrued expenses and deferred rent	6,194	4,310
Notes payable, net of discount, current		5,545
Total current liabilities	9,159	13,426
Deferred rent, long-term	3,221	3,387
Notes payable, net of discount, long-term	24,788	12,471
Total liabilities	37,168	29,284
Commitments and contingencies (Note 13)
Stockholders' equity:
Preferred stock, $0.0001 par value; 5,000,000 shares authorized and no shares issued or outstanding at December 31, 2018 and December 31, 2017, respectively
Common stock, $0.0001 par value; 100,000,000 shares authorized and 41,518,091 and 29,658,202 shares issued and outstanding at December 31, 2018 and December 31, 2017	4	3
Additional paid-in capital	333,114	263,409
Accumulated deficit	(297,243)	(237,265)
Total stockholders' equity	35,875	26,147
Total liabilities and stockholders' equity	$ 73,043	$ 55,431

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2018	Dec. 31, 2017
Consolidated Balance Sheets
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	41,518,091	29,658,202
Common stock, shares outstanding	41,518,091	29,658,202

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue:
Total revenue	$ 1,990	$ 1,923	$ 1,887
Costs and operating expenses:
Research and development	36,915	30,880	27,065
Selling and marketing	4,942	17,000	6,701
General and administrative	18,786	15,509	11,004
Total costs and operating expenses	61,108	63,846	45,213
Loss from operations	(59,118)	(61,923)	(43,326)
Other income (expense):
Interest income	879	424	304
Interest expense	(1,739)	(1,892)	(1,680)
Other income (expense), net		5	(1)
Total other expense, net	(860)	(1,463)	(1,377)
Net loss	$ (59,978)	$ (63,386)	$ (44,703)
Net loss per share, basic and diluted	$ (1.57)	$ (2.20)	$ (1.80)
Weighted average common shares outstanding, basic and diluted	38,115,142	28,818,196	24,816,348
Comprehensive loss:
Net loss	$ (59,978)	$ (63,386)	$ (44,703)
Other comprehensive loss:
Unrealized gain on marketable securities		5	63
Total other comprehensive income		5	63
Total comprehensive loss	(59,978)	(63,381)	(44,640)
Product
Revenue:
Total revenue	1,990	1,923	1,845
Costs and operating expenses:
Cost of product revenue	$ 465	$ 457	443
Collaboration revenue
Revenue:
Total revenue			$ 42

Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Loss	Total
Balance at Dec. 31, 2015	$ 2	$ 218,830	$ (129,176)	$ (68)	$ 89,588
Balance, shares at Dec. 31, 2015	24,750,281
Stockholders' Equity
Issuance of common stock upon exercise of stock options		199			199
Issuance of common stock upon exercise of stock options, shares	105,114
Issuance of common stock in connection with employee stock purchase plan		278			278
Issuance of common stock in connection with employee stock purchase plan, shares	66,628
Issuance of common stock upon public offering, net of issuance costs	$ 1	626			627
Issuance of common stock upon public offering, net of issuance costs, shares	102,077
Unrealized gain on marketable securities				63	63
Stock-based compensation expense		5,956			5,956
Net loss			(44,703)		(44,703)
Balance at Dec. 31, 2016	$ 3	225,889	(173,879)	(5)	52,008
Balance, shares at Dec. 31, 2016	25,024,100
Stockholders' Equity
Issuance of common stock upon exercise of stock options		685			685
Issuance of common stock upon exercise of stock options, shares	220,520
Issuance of common stock in connection with employee stock purchase plan		276			276
Issuance of common stock in connection with employee stock purchase plan, shares	53,662
Issuance of common stock upon public offering, net of issuance costs		29,238			29,238
Issuance of common stock upon public offering, net of issuance costs, shares	4,359,920
Unrealized gain on marketable securities				$ 5	5
Stock-based compensation expense		7,321			7,321
Net loss			(63,386)		(63,386)
Balance at Dec. 31, 2017	$ 3	263,409	(237,265)		26,147
Balance, shares at Dec. 31, 2017	29,658,202
Stockholders' Equity
Issuance of common stock upon exercise of stock options		397			$ 397
Issuance of common stock upon exercise of stock options, shares	182,261				182,261
Issuance of common stock in connection with employee stock purchase plan		297			$ 297
Issuance of common stock in connection with employee stock purchase plan, shares	81,455
Issuance of common stock upon public offering, net of issuance costs	$ 1	61,528			61,529
Issuance of common stock upon public offering, net of issuance costs, shares	11,596,173
Stock-based compensation expense		7,483			7,483
Net loss			(59,978)		(59,978)
Balance at Dec. 31, 2018	$ 4	$ 333,114	$ (297,243)		$ 35,875
Balance, shares at Dec. 31, 2018	41,518,091

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities:
Net loss	$ (59,978)	$ (63,386)	$ (44,703)
Adjustments to reconcile net loss to net cash used in operating activities
Stock-based compensation expense	7,483	7,321	5,956
Non-cash interest expense	397	408	371
Depreciation and amortization expense	2,286	1,625	881
(Gain)/loss on disposal of property and equipment		(5)	1,269
Purchase of premium on marketable securities		(3)	(37)
Amortization of premium on marketable securities		17	186
Changes in operating assets and liabilities:
Accounts receivable	25	24	(57)
Prepaid expenses and other current assets	(260)	45	924
Inventory	(95)	(9)	21
Accounts payable	(796)	932	(159)
Accrued expenses and deferred rent	1,711	2,558	1,389
Deferred revenue			(42)
Net cash used in operating activities	(49,227)	(50,473)	(34,001)
Cash flows from investing activities:
Purchases of property and equipment	(1,889)	(8,252)	(1,919)
Proceeds from sale of property and equipment		5	2
Purchases of marketable securities		(3,000)	(41,699)
Proceeds from maturities of marketable securities		38,200	80,684
Net cash (used in) provided by investing activities	(1,889)	26,953	37,068
Cash flows from financing activities:
Proceeds from issuance of notes payable	12,032	3,700
Proceeds from exercise of stock options	397	685	199
Proceeds from issuance of common stock pursuant to employee stock purchase plan	297	276	278
Proceeds from issuance of common stock offering, net	61,571	29,238	627
Payments of insurance costs financed by a third party		(591)	(519)
Repayment of notes payable	(5,657)	(1,300)
Net cash provided by financing activities	68,640	32,008	585
Net increase in cash, cash equivalents and restricted cash	17,524	8,488	3,652
Cash, cash equivalents and restricted cash at beginning of period	43,152	34,664	31,012
Cash, cash equivalents and restricted cash at end of period	60,676	43,152	34,664
Supplemental disclosure of cash flow information:
Cash paid for interest	1,515	1,461	1,301
Supplemental disclosure of non-cash investing and financing activities:
Additions to property and equipment included in accounts payable and accrued expenses at balance sheet dates	155	538	451
Insurance premium financed by a third party			$ 722
Public offering costs included in accounts payable and accrued expenses at balance sheet dates	$ 42	$ 108

Nature of the Business and Basis of Presentation	12 Months Ended
Nature of the Business and Basis of Presentation	Dec. 31, 2018
Nature of the Business and Basis of Presentation
Nature of the Business and Basis of Presentation	OCULAR THERAPEUTIX, INC. NOTES TO CONSOLIDATED FINANCIAL STATEMENTS (Amounts in thousands, except share and per share data) 1. Nature of the Business and Basis of Presentation Ocular Therapeutix, Inc. (the “Company”) was incorporated on September 12, 2006 under the laws of the State of Delaware. The Company is a biopharmaceutical company focused on the formulation, development and commercialization of innovative therapies for diseases and conditions of the eye using its proprietary, bioresorbable hydrogel platform technology. The Company’s product pipeline candidates are provide differentiated drug delivery solutions that reduce the complexity and burden of the current standard of care by creating local programmed-release alternatives. Since inception, the Company’s operations have been primarily focused on organizing and staffing the Company, acquiring rights to intellectual property, business planning, raising capital, developing its technology, identifying potential product candidates, undertaking preclinical studies and clinical trials, manufacturing initial quantities of its products and product candidates and building the initial sales and marketing infrastructure for the commercialization of the Company’s approved products and product candidates. The Company is subject to risks common to companies in the biotechnology industry including, but not limited to, new technological innovations, protection of proprietary technology, dependence on key personnel, compliance with government regulations, regulatory approval, uncertainty of market acceptance of products and the need to obtain additional financing. Product candidates currently under development will require significant additional research and development efforts, including extensive preclinical and clinical testing and regulatory approval, prior to commercialization. As of December 31, 2018, the Company’s lead product candidate DEXTENZA (dexamethasone insert) 0.4mg, has been approved by the FDA and the other product candidates are in clinical stage development. There can be no assurance that the Company’s research and development will be successfully completed, that adequate protection for the Company’s intellectual property will be obtained, that any products developed will obtain necessary government regulatory approval and adequate reimbursement or that any approved products will be commercially viable. Even if the Company’s product development efforts are successful, it is uncertain when, if ever, the Company will generate significant revenue from product sales. The Company operates in an environment of rapid change in technology and substantial competition from pharmaceutical and biotechnology companies. In addition, the Company is dependent upon the services of its employees and consultants. The Company may not be able to generate significant revenue from sales of any product for several years, if at all. Accordingly, the Company will need to obtain additional capital to finance its operations, including to support the planned commercial launch of DEXTENZA. The Company believes that its existing cash and cash equivalents at December 31, 2018 along with the net proceeds of $37,100 from the issuance of convertible notes payable issued in March 2019 (Note 19) and the $4,967 net proceeds obtained from the issuance of common stock in January and February 2019 (Note 19), will enable it to fund its operating expenses, debt service obligations and capital expenditure requirements into early 2020. Management has determined that the Company’s accumulated deficit, history of losses, negative cash flows from operations and future expected losses raise substantial doubt about the Company’s ability to continue as a going concern within one year of the issuance date of these consolidated financial statements. The Company expects to continue to generate operating losses and negative cash flows from operations in the foreseeable future. As of December 31, 2018, the Company had an accumulated deficit of $297,243. While the Company has raised capital in the past, the ability to raise capital in future periods is not considered probable, as defined under the accounting standards and therefore, were not considered in management’s assessment of the Company’s ability to continue as a going concern. The Company expects to seek additional funds through equity or debt financings. If the Company is unable to obtain other financing, the Company would be forced to delay, reduce or eliminate its research and development programs or any future commercialization efforts or to relinquish valuable rights to its technologies, future revenue streams, research programs or product candidates or grant licenses on terms that may not be favorable to the Company. The actions necessary to reduce spending to a level that mitigates the factors described above are not considered probable, as defined in the accounting standards and therefore were not considered in management’s assessment of the Company’s ability to continue as a going concern. The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”).

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2018

Summary of Significant Accounting Policies

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Basis of Presentation and Principles of Consolidation

The accompanying consolidated financial statements reflect the operations of the Company and its wholly-owned subsidiary. All intercompany accounts and transactions have been eliminated.

Use of Estimates

The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements, and the reported amounts of revenues and expenses during the reporting periods. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, revenue recognition, the accrual of research and development expenses, including clinical trials, and the valuation of common stock and stock-based awards. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Actual results could differ from the Company’s estimates.

Cash Equivalents

The Company considers all short-term, highly liquid investments with original maturities of ninety days or less at date of purchase to be cash equivalents. Cash equivalents, which primarily consist of money market accounts, are stated at fair value.

Revenue Recognition

On January 1, 2018, the Company adopted the new revenue standard, Accounting Standards Codification (“ASC”) 606 – Revenue from Contracts with Customers, which amended revenue recognition principles and provides a single, comprehensive set of criteria for revenue recognition within and across all industries. The Company’s adoption of the new revenue standard did not have a material impact on its consolidated financial statements. This new revenue standard applies to all contracts with customers, except for contracts that are within the scope of other standards, such as leases, insurance, collaboration arrangements and financial instruments. The new revenue standard provides a five-step framework whereby revenue is recognized when control of promised goods or services is transferred to a customer at an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. To determine revenue recognition for arrangements that the Company determines are within the scope of the new revenue standard, the Company performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) we satisfy a performance obligation. The Company only applies the five-step model to contracts when collectability of the consideration to which the Company is entitled in exchange for the goods or services the Company transfers to the customer is determined to be probable. At contract inception, once the contract is determined to be within the scope of the new revenue standard, the Company assess whether the goods or services promised within each contract are distinct and, therefore, represent a separate performance obligation. Goods and services that are determined not to be distinct are combined with other promised goods and services until a distinct bundle is identified. The Company then allocates the transaction price (the amount of consideration the Company expects to be entitled to from a customer in exchange for the promised goods or services) to each performance obligation and recognizes the associated revenue when (or as) each performance obligation is satisfied.

Amounts are recorded as accounts receivable when the Company’s right to consideration is unconditional. The Company does do not assess whether a contract has a significant financing component if the expectation at contract inception is that the period between payment by the customer and the transfer of the promised goods or services to the customer will be one year or less. The Company expenses incremental costs of obtaining a contract as and when incurred if the expected amortization period of the asset that the Company would have recognized is one year or less or the amount is immaterial. At December 31, 2018, the Company had not capitalized any costs to obtain any of our contracts.

The Company recognizes revenue on product sales at the time control of the product transfers to the customer. In substantially all of the Company’s arrangements, title of its products transfers at shipping point and, as a result, the Company determined control transfers at the point of shipment. In more limited cases, there are destination-based shipping terms and, thus, control is deemed to transfer when the product arrives at the customer site. Incremental costs of obtaining a contract are expensed as and when incurred if the expected amortization period of the asset that would have been recognized is one year or less. Shipping and handling costs are included as a component of cost of product revenue.

Payment terms and conditions vary among the Company’s customers, although terms generally include a requirement of payment within 30 days of product shipment. Prior to providing payment terms to customers, an evaluation of the customer’s credit risk is performed. Returns and customer credits are infrequent and insignificant and are recorded as a reduction to sales. Rights of return are not included in sales arrangements and, therefore, there is minimal variable consideration included in the transaction price of our products.

Inventory Valuation

Inventory is valued at the lower of cost or net realizable value, determined by the first-in, first-out (“FIFO”) method.

Prior to approval by the Food and Drug Administration (“FDA”) or other regulatory agencies of the Company’s products, the Company expenses inventory costs in the period incurred as research and development expenses. After such time as the product receives approval, the Company begins to capitalize the inventory costs related to the product. The Company also reviews its inventories for potential obsolescence.

Inventory consisted of the following:


	December 31,
	2018		2017
Raw materials	$	112	$	68
Work-in-process		33		37
Finished goods		72		17
	$	217	$	122

Restricted Cash

As of December 31, 2018 and 2017, the Company held restricted cash of $6,614 and $1,614, respectively, on its consolidated balance sheet. The Company held restricted cash as security deposits for the lease of its manufacturing space and corporate headquarters (Note 13). In 2018, restricted cash increased due to a financial covenant associated with the 2018 Amended Credit Facility which restricts the Company's withdrawal or usage of $5,000.

Concentration of Credit Risk and of Significant Suppliers

Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash and cash equivalents. The Company has all cash and cash equivalents balances at one accredited financial institution, in amounts that exceed federally insured limits. The Company does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships.

The Company is dependent on a small number of third-party manufacturers to supply products for research and development activities in its preclinical and clinical programs and for sales of its ReSure Sealant product. The Company’s development programs as well as revenue from future sales of ReSure Sealant could be adversely affected by a significant interruption in the supply of any of the components of these products.

Fair Value Measurements

Certain assets and liabilities are carried at fair value under GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable:

Level 1—Quoted prices in active markets for identical assets or liabilities.

Level 2—Observable inputs (other than Level 1 quoted prices) such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data.

Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques.

The Company’s cash equivalents are carried at fair value determined according to the fair value hierarchy described above (Note 3). The carrying value of accounts receivable, accounts payable and accrued expenses approximate their fair value due to the short-term nature of these assets and liabilities. At December 31, 2018 and 2017, the carrying value of the Company’s outstanding notes payable (Note 7) approximates fair value based on the interest rate for the borrowings outstanding.

Property and Equipment

Property and equipment are stated at cost less accumulated depreciation. Depreciation expense is recognized using the straight-line method over a three- to five-year estimated useful life. Leasehold improvements are amortized over the shorter of the lease term or the estimated useful life of the related asset. Expenditures for repairs and maintenance of assets are charged to expense as incurred. Upon retirement or sale, the cost and related accumulated depreciation of assets disposed of are removed from the accounts and any resulting gain or loss is included in loss from operations.

Impairment of Long-Lived Assets

Long-lived assets consist of property and equipment. Long-lived assets to be held and used are tested for recoverability whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends, and significant changes or planned changes in the use of the assets. If an impairment review is performed to evaluate a long-lived asset for recoverability, the Company compares forecasts of undiscounted cash flows expected to result from the use and eventual disposition of the long-lived asset to its carrying value. An impairment loss would be recognized when estimated undiscounted future cash flows expected to result from the use of an asset are less than its carrying amount. The impairment loss would be based on the excess of the carrying value of the impaired asset over its fair value, determined based on discounted cash flows. The Company has had no impairment triggers of long-lived assets.

Research and Development Costs

Research and development costs are expensed as incurred. Included in research and development expenses are salaries, stock-based compensation and benefits of employees and other operational costs related to the Company’s research and development activities, including external costs of outside vendors engaged to conduct preclinical studies and clinical trials, manufacturing costs of the Company’s products prior to regulatory approval, costs related to collaboration agreements and facility-related expenses.

Research Contract Costs and Accruals

The Company has entered into various research and development contracts with research institutions and other companies both inside and outside of the United States. Certain of these agreements have cancellation clauses, and related payments are recorded as research and development expenses as incurred. The Company records accruals for estimated ongoing research costs. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the studies, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates are made in determining the accrued balances at the end of any reporting period. Actual results could differ from the Company’s estimates. The Company’s historical accrual estimates have not been materially different from the actual costs.

Patent Costs

All patent-related costs incurred in connection with filing and prosecuting patent applications are recorded as general and administrative expenses as incurred, as recoverability of such expenditures is uncertain.

Accounting for Stock-Based Compensation

The Company measures all stock options and other stock-based awards granted to employees and directors at the fair value on the date of the grant using the Black-Scholes option-pricing model. The fair value of the awards is recognized as expense, net of estimated forfeitures, over the requisite service period, which is generally the vesting period of the respective award. The straight-line method of expense recognition is applied to all awards with service-only conditions.

For stock-based awards granted to consultants and non-employees, compensation expense is recognized over the period during which services are rendered by such consultants and non-employees until completed. At the end of each financial reporting period prior to completion of the service, the fair value of these awards is re-measured using the then-current fair value of the Company’s common stock and updated assumption inputs in the Black-Scholes option-pricing model.

The Company classifies stock-based compensation expense in its consolidated statement of operations and comprehensive loss in the same manner in which the award recipient’s payroll costs are classified or in which the award recipient’s service payments are classified.

The Company recognizes compensation expense for only the portion of awards that are expected to vest. In developing a forfeiture rate estimate, the Company has considered its historical experience to estimate pre-vesting forfeitures for service-based awards. The impact of a forfeiture rate adjustment will be recognized in full in the period of adjustment, and if the actual forfeiture rate is materially different from the Company’s estimate, the Company may be required to record adjustments to stock-based compensation expense in future periods.

Income Taxes

The Company accounts for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the consolidated financial statements or in the Company’s tax returns. Deferred taxes are determined based on the difference between the financial statement and tax basis of assets and liabilities using enacted tax rates in effect in the years in which the differences are expected to reverse. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. The Company assesses the likelihood that its deferred tax assets will be recovered from future taxable income and, to the extent it believes, based upon the weight of available evidence, that it is more likely than not that all or a portion of deferred tax assets will not be realized, a valuation allowance is established through a charge to income tax expense.

The Company accounts for uncertainty in income taxes recognized in the consolidated financial statements by applying a two-step process to determine the amount of tax benefit to be recognized. First, the tax position must be evaluated to determine the likelihood that it will be sustained upon external examination by the taxing authorities. If the tax position is deemed more-likely-than-not to be sustained, the tax position is then assessed to determine the amount of benefit to recognize in the consolidated financial statements. The amount of the benefit that may be recognized is the largest amount that has a greater than 50% likelihood of being realized upon ultimate settlement. The provision for income taxes includes the effects of any resulting tax reserves, or unrecognized tax benefits, that are considered appropriate as well as the related net interest and penalties.

Segment Data

The Company manages its operations as a single segment for the purposes of assessing performance and making operating decisions. The Company’s singular focus is on advancing its bioresorbable hydrogel product candidates for the programed-release delivery of therapeutic agents, specifically for ophthalmology. All tangible assets are held in the United States.

Comprehensive Loss

Comprehensive loss includes net loss as well as other changes in stockholders’ equity that result from transactions and economic events other than those with stockholders. For the years ended December 31, 2017 and 2016, other comprehensive loss consisted of unrealized gains (losses) from marketable securities. For the years ended December 31, 2018, there were no items that gave rise to other comprehensive loss and therefore, was no difference between net loss and comprehensive loss.

Net Income (Loss) Per Share

The Company applies the two-class method which determines net income (loss) per share for each class of common and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method requires income available to common stockholders for the period to be allocated between common and participating securities based upon their respective rights to receive dividends as if all income for the period had been distributed.

Basic net income (loss) per share attributable to common stockholders is computed by dividing the net income (loss) attributable to common stockholders by the weighted average number of shares of common stock outstanding for the period. Diluted net income (loss) attributable to common stockholders is computed by adjusting income (loss) attributable to common stockholders to reallocate undistributed earnings based on the potential impact of dilutive securities, including outstanding stock options, unvested restricted common stock, common stock warrants. Diluted net income (loss) per share attributable to common stockholders is computed by dividing the diluted net income (loss) attributable to common stockholders by the weighted average number of common shares outstanding for the period, including potential dilutive common shares assuming the dilutive effect of outstanding stock options, common stock warrants and unvested restricted common stock.

Restricted stock awards granted by the Company entitle the holder of such awards to dividends declared or paid by the board of directors, regardless of whether such awards are unvested, as if such shares were outstanding common shares at the time of the dividend. However, the unvested restricted stock awards are not entitled to share in the residual net assets (deficit) of the Company. Accordingly, in periods in which the Company reports a net loss attributable to common stockholders, diluted net loss per share attributable to common stockholders is the same as basic net loss per share attributable to common stockholders, since dilutive common shares are not assumed to have been issued if their effect is anti-dilutive. The Company reported a net loss attributable to common stockholders for the years ended December 31, 2018, 2017 and 2016.

Deferred Offering Costs

The Company capitalizes certain legal and other third-party fees that are directly associated with in-process equity financings as deferred offering costs until such financings are consummated. After consummation of the equity financing, these costs are recorded as a reduction of the proceeds generated as a result of the offering. Should the planned equity financing be abandoned, the deferred offering costs will be expensed immediately as a charge to operating expense in the consolidated statements of operations and comprehensive loss. There were no deferred offering costs at December 31, 2018. Deferred offering costs amounted to $108 at December 31, 2017 and are capitalized in prepaid expenses and other current assets.

Recently Adopted Accounting Pronouncements

In March 2016, the FASB issued ASU No. 2016-09, Compensation – Stock Compensation (“ASU 2016-09”). ASU 2016-09 identifies areas for simplification involving several aspects of accounting for share-based payment transactions, including the income tax consequences, classification of awards as either equity or liabilities, an option to recognize gross stock compensation expense with actual forfeitures recognized as they occur, as well as certain classifications on the statement of cash flows. The amendments in this update became effective for the first interim period within annual reporting periods beginning after December 15, 2016. The Company adopted ASU 2016-09 on January 1, 2017 and continues to estimate forfeitures at each period. The adoption of ASU 2016-09 did not have a material impact to the consolidated financial statements.

The Company adopted the New Revenue Standard on January 1, 2018 using the modified retrospective method. The adoption of the New Revenue Standard did not have a material impact on its consolidated financial statements. Under the New Revenue Standard, the Company recognizes revenue when the customer obtains control of the good in an amount that reflects the consideration which the Company expects to receive in exchange for those goods. The Company only applies the New Revenue Standard to contracts when it is probable that the Company will collect the consideration it is entitled to in exchange for the goods transferred to the customer.

In August 2016, the FASB issued Accounting Standards Update No. 2016-15, Classification of Certain Cash Receipts and Cash Payments (“ASU 2016-15”). ASU 2016-15 is intended to clarify guidance on the classification of certain cash receipts and payments in the statement of cash flows and to eliminate the diversity in practice related to such classifications. The Company adopted ASU 2016-15 effective January 1, 2018 and its adoption did not have a material impact on its consolidated financial statements.

In November 2016, the FASB issued ASU 2016-18, “Statement of Cash Flows (Topic 230) - Restricted Cash” (“ASU 2016-18”). ASU 2016-18 requires a statement of cash flows to explain the change during the period in the total of cash, cash equivalents, and amounts generally described as restricted cash or restricted cash equivalents. Amounts generally described as restricted cash and restricted cash equivalents should be included with cash and cash equivalents

when reconciling the beginning-of-period and end-of- period total amounts shown on the statement of cash flows. The Company adopted ASU 2016-18 effective January 1, 2018 and has reflected the adoption retrospectively to all periods presented. The Company’s statements of cash flows includes restricted cash with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on such statements. A reconciliation of the cash, cash equivalents, and restricted cash reported within the consolidated balance sheet that sum to the total of the same amounts shown in the consolidated statement of cash flows:


	December 31,		December 31,		December 31,
	2018		2017		2016
Cash and cash equivalents	$	54,062	$	41,538	$	32,936
Restricted cash		6,614		1,614		1,728
Total cash, cash equivalents and restricted cash as shown on the statement of cash flow	$	60,676	$	43,152	$	34,664

In May 2017, the FASB issued ASU 2017-09, “Compensation-Stock Compensation (Topic 718): Scope of Modification Accounting” (“ASU 2017-09”), which clarifies when to account for a change to the terms or conditions of a share-based payment award as a modification. The new standard does not change the accounting for modifications but clarifies that modification accounting guidance should only be applied if the fair value, vesting conditions, or classification of the award changes as a result of the change in terms or conditions. The new standard is effective for fiscal years, and interim periods within, beginning after December 15, 2017. Early adoption is permitted. A reporting entity must apply the amendments in the ASU prospectively to an award modified on or after the adoption date. The Company adopted ASU 2017-09 effective January 1, 2018 and its adoption did not have a material impact on the Company’s consolidated financial statements. The adoption of ASU 2017-09 will have an impact on the accounting for the modification of stock-based awards, if any, to the extent stock-based awards are modified.

Recently Issued Accounting Pronouncements

In February 2016, the FASB issued ASU No. 2016-02, Leases (ASC 842) (“ASU 2016-02”). ASU 2016-02 requires lessees to recognize most leases on the balance sheet. This is expected to increase both reported assets and liabilities. The new lease standard does not substantially change lessor accounting. The Company adopted the new leasing standard on January 1, 2019, using a modified retrospective transition approach to be applied to leases existing as of, or entered into after, January 1, 2019. The Company elected to apply the package of practical expedients which allows entities not to reassess whether contracts are or contain leases, lease classification, and whether initial direct costs qualify for capitalization. Additionally, the Company elected not to separate lease and non-lease components. The Company’s primary operating leases represent the lease of its corporate headquarters at 15 Crosby and a lease for additional space at 36 Crosby, both in Bedford, Massachusetts. Upon adoption of the new leasing standard, the Company expects to recognize a lease liability of approximately $9,000 and a related right-of-use asset of approximately $6,000 on its consolidated balance sheet with the difference being due to the elimination of previously reported lease incentive obligations and deferred rent. The impact of adoption of the new leasing standards will have an immaterial impact to the Company’s consolidated statements of operations and comprehensive loss and cash flows.

Fair Value of Financial Assets and Liabilities

12 Months Ended

Dec. 31, 2018

Fair Value of Financial Assets and Liabilities

Fair Value of Financial Assets and Liabilities

3. Fair Value of Financial Assets and Liabilities

The following tables present information about the Company’s financial assets and liabilities that are measured at fair value on a recurring basis as of December 31, 2018 and 2017 and indicate the level of the fair value hierarchy utilized to determine such fair value:


	Fair Value Measurements as of
	December 31, 2018 Using:
	Level 1		Level 2		Level 3		Total
Assets:
Cash equivalents:
Money market funds	$	—	$	50,906	$	—	$	50,906
Total	$	—	$	50,906	$	—	$	50,906


	Fair Value Measurements as of
	December 31, 2017 Using:
	Level 1		Level 2		Level 3		Total
Assets:
Cash equivalents:
Money market funds	$	—	$	40,386	$	—	$	40,386
Total	$	—	$	40,386	$	—	$	40,386

During the years ended December 31, 2018, 2017 and 2016, there were no transfers between Level 1, Level 2 and Level 3.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Property and Equipment, net

12 Months Ended

Dec. 31, 2018

Property and Equipment, net

Property and Equipment, net

4. Property and Equipment, net

Property and equipment, net consisted of the following:


	December 31,
	2018		2017
Equipment	$	7,917	$	6,183
Leasehold improvements		8,675		8,553
Furniture and fixtures		760		740
Software		180		118
Construction in progress		331		225
		17,863		15,819
Less: Accumulated depreciation		(7,627)		(5,341)
	$	10,236	$	10,478

Depreciation expense was $2,286, $1,625 and $881 for the years ended December 31, 2018, 2017 and 2016, respectively.

For the year ended December 31, 2016, the Company wrote off $1,263 of manufacturing equipment that was included in construction in progress at December 31, 2015.

Accrued Expenses and Deferred Rent

12 Months Ended

Dec. 31, 2018

Accrued Expenses and Deferred Rent

Accrued Expenses and Deferred Rent

5. Accrued Expenses and Deferred Rent

Accrued expenses consisted of the following:


	December 31,		December 31,
	2018		2017
Accrued payroll and related expenses	$	3,558	$	2,936
Accrued rent		267		267
Accrued professional fees		1,393		534
Accrued research and development expenses		380		217
Accrued other		596		356
	$	6,194	$	4,310

Collaboration and Feasibility Agreements	12 Months Ended
Collaboration and Feasibility Agreements	Dec. 31, 2018
Collaboration and Feasibility Agreements
Collaboration and Feasibility Agreements	6. Collaboration and Feasibility Agreements On October 10, 2016, the Company entered into a Collaboration, Option and License Agreement (the “Collaboration Agreement”) with Regeneron Pharmaceuticals, Inc. (“Regeneron”) for the development and potential commercialization of products using the Company’s hydrogel in combination with Regeneron’s large molecule VEGF-targeting compounds for the treatment of retinal diseases. The Collaboration Agreement does not cover the development of any products that deliver small molecule drugs, including TKIs for any target including VEGF, or any product that deliver large molecule drugs other than those that target VEGF proteins. Under the terms of the Collaboration Agreement, the Company and Regeneron have agreed to conduct a joint research program with the aim of developing a sustained-release formulation of aflibercept, currently marketed under the tradename Eylea, that is suitable for advancement into clinical development. The Company has granted Regeneron an option (the “Option”) to enter into an exclusive, worldwide license under its intellectual property to develop and commercialize products using the Company’s hydrogel in combination with Regeneron’s large molecule VEGF-targeting compounds (“Licensed Products”). Under the term of the Collaboration Agreement, Regeneron is responsible for funding an initial preclinical tolerability study, which it initiated in early 2018. If Regeneron decided to exercise the Option, Regeneron will conduct further preclinical development and an initial clinical trial under a collaboration plan. The Company is obligated to reimburse Regeneron for certain development costs incurred by Regeneron under the collaboration plan during the period through the completion of the initial clinical trial, subject to a cap of $25,000, which cap may be increased by up to $5,000 under certain circumstances. If Regeneron elects to proceed with further development following the completion of the collaboration plan, it will be solely responsible for conducting and funding further development and commercialization of product candidates. If the Option is exercised, Regeneron is required to use commercially reasonable efforts to research, develop and commercialize at least one Licensed Product. Such efforts shall include initiating the dosing phase of a subsequent clinical trial within specified time periods following the completion of the first-in-human clinical trial or the initiation of preclinical toxicology studies, subject to certain extensions. Under the terms of the Collaboration Agreement, Regeneron has agreed to pay the Company $10,000 upon the exercise of the Option. In December 2017, the Company delivered to Regeneron the final formulation for Regeneron’s initial preclinical tolerability study. Although the Company is engaged in ongoing discussions with Regeneron, Regeneron has not informed the Company of its decision to exercise the Option. Pending a decision from Regeneron, the Company is not actively pursuing further formulation development or other preclinical testing under the Collaboration Agreement. The Company is also eligible to receive up to $145,000 per Licensed Product upon the achievement of specified development and regulatory milestones, $100,000 per Licensed Product upon first commercial sale of such Licensed Product and up to $50,000 based on the achievement of specified sales milestones for all Licensed Products. In addition, the Company is entitled to tiered, escalating royalties, in a range from a high-single digit to a low-to-mid teen percentage of net sales of Licensed Products.

Notes Payable

12 Months Ended

Dec. 31, 2018

Notes Payable.

Notes Payable

7. Notes Payable

The Company entered into a credit and security agreement in 2014 (the “2014 Credit Facility”) which most recently was amended in March 2017 and in December 2018 has a total borrowing capacity of $25,000 which has been fully drawn down.

In March 2017, the Company amended (the “2017 Amended Credit Facility”) the terms of its debt with existing lenders for total indebtedness of $18,000, which was used primarily to pay-off outstanding balances as of the closing date. The interest only period was extended through February 1, 2018. The Company was obligated to make interest-only payments under the 2017 Amended Credit Facility until February 1, 2018. Thereafter, it was required to make monthly principal and interest payments through December 1, 2020. Amounts borrowed under the Amended Credit Facility were at LIBOR base rate, subject to 1.00% floor, plus 7.25% with an indicative interest rate of 8.25% as of the amendment date. In addition, a final payment equal to 3.5% of amounts drawn under the Amended Credit Facility was due upon the maturity date of December 1, 2020.

In December 2018, the Company amended (the “2018 Amended Credit Facility”) the terms of its debt with existing lenders for total indebtedness of $25,000, which was used primarily to pay-off outstanding balances as of the closing date. The Company is required to make interest-only payments under the 2018 Amended Credit Facility until December 2020. Commencing in January 2021, the Company is required to make 36 equal monthly installments of principal in the amount of $694, plus interest, through December 2023. In the event the Company achieves certain milestones under the 2018 Amended Credit Facility, the Company has the right to extend the interest-only payments through December 21, 2021 and make 24 equal monthly installments of principal in the amount of $1,042, plus interest. The Company has not assumed the achievement of these milestones for purposes of disclosures herein.

Amounts borrowed under the 2018 Amended Credit Facility are at LIBOR base rate, subject to 2.00% floor, plus 7.25%. The interest rate on the date of the amendment was 9.76%. In addition, a final payment (exit fee) equal to 3.5% of amounts drawn under the Amended Credit Facility, or $875 based on borrowings of $25,000, is due upon the maturity date of December 21, 2023. The Company is accruing the exit fee through December 21, 2023.

The Company accounted for the 2017 and 2018 Amended Credit Facility as a modification in accordance with the guidance in ASC 470-50, Debt. Amounts paid to the lenders were recorded as debt discount and a new effective interest rate was established. The effective annual interest rate of the outstanding debt under the Amended Credit Facility is 13.9%.

Under the 2018 Amended Credit Facility the Company is required to maintain a minimum of $5,000 of cash on hand as a financial covenant to the borrowing arrangement, which the Company has included in long-term restricted cash in the accompanying consolidated balance sheet. There are no other financial covenants associated with the 2018 Amended Credit Facility; however, there are negative covenants restricting the Company’s activities, including limitations on dispositions, mergers or acquisitions; encumbering its intellectual property; incurring indebtedness or liens; paying dividends; making certain investments; and engaging in certain other business transactions. The Company is not in violation of any of the covenants. The obligations under the 2018 Amended Credit Facility are subject to acceleration upon the occurrence of specified events of default, including a material adverse change in the Company’s business, operations or financial or other condition. The debt is collateralized by substantially all of the Company’s assets, including its intellectual property.

Borrowings outstanding are as follows:


	December 31, 2018		December 31, 2017
Borrowings outstanding	$	25,000	$	18,000
Accrued exit fee		5		221
Unamortized discount		(217)		(205)
	$	24,788	$	18,016

As of December 31, 2018, the annual repayment requirements for the 2018 Amended Credit Facility, inclusive of interest and the final payment of $875 due at expiration, were as follows:



			Interest and
Year Ending December 31,	Principal		Final Payment		Total
2019	$	—	$	2,474	$	2,474
2020		—		2,481		2,481
2021		8,333		2,094		10,427
2022		8,333		1,270		9,603
2023		8,334		1,319		9,653
	$	25,000	$	9,638	$	34,638

Warrants	12 Months Ended
Warrants	Dec. 31, 2018
Warrants
Warrants	8. Warrants The Company has warrants for the purchase of 18,939 shares of common stock outstanding at December 31, 2018 at a weighted average exercise price of $7.92 per share and an expiration date of April 17, 2021.

Preferred Stock	12 Months Ended
Preferred Stock	Dec. 31, 2018
Preferred Stock
Preferred Stock	9. Preferred Stock The Amended and Restated Certificate of Incorporation authorized 5,000,000 shares of preferred stock, $0.0001 par value, all of which is undesignated and none of which are issued or outstanding at December 31, 2018.

Common Stock	12 Months Ended
Common Stock	Dec. 31, 2018
Common Stock
Common Stock	10. Common Stock The Amended and Restated Certificate of Incorporation authorized 100,000,000 shares of the Company’s common stock. Each share of common stock entitles the holder to one vote on all matters submitted to a vote of the Company’s stockholders. In November 2016, the Company entered into a controlled equity offering sales agreement, (the “2016 Sales Agreement”) with Cantor Fitzgerald & Co., (“Cantor”), under which the Company may offer and sell its common stock having aggregate proceeds of up to $40,000 may be sold from time to time. During the fourth quarter of 2016, the Company sold 102,077 shares of common stock under the 2016 Sales Agreement resulting in net proceeds of approximately $626 after underwriting discounts, commission and other offering expenses. During the year ended December 31, 2017, the Company sold 788,491 shares of common stock under the 2016 Sales Agreement, resulting in net proceeds of approximately $5,977 after underwriting discounts and commissions. During the year ended December 31, 2018, the Company sold 4,121,173 shares of common stock under the 2016 Sales Agreement, resulting in net proceeds of approximately $26,824 after underwriting discounts, commissions and expenses. Through December 31, 2018, the Company has sold 5,011,741 shares of common stock at-the-market under the 2016 Sales Agreement, resulting in net proceeds of approximately $33,427 after underwriting discounts, commissions and expenses. In January 2017, the Company completed a follow-on offering of its common stock at a public offering price of $7.00 per share. The offering consisted of 3,571,429 shares of common stock sold by the Company. The Company received net proceeds from the follow-on offering of $23,261 after deducting underwriting discounts, commissions and expenses. In January 2018, the Company completed a follow-on offering of its common stock at a public offering price of $5.00 per share. The offering consisted of 7,475,000 shares of common stock sold by the Company, including those shares sold in connection with the exercise by the underwriter of its option to purchase additional shares. The Company received net proceeds from the follow-on offering of $34,704 after deducting underwriting discounts, commissions and expenses. As of December 31, 2018, the Company had reserved 7,232,523 shares of common stock for the exercise of outstanding stock options and the number of shares remaining available for grant under the Company’s 2014 Stock Incentive Plan (the “2014 Plan”), the number of shares available for issuance under the 2014 Employee Stock Purchase Plan (Note 11), and the outstanding warrants to purchase common stock (Note 8).

Stock-Based Awards

12 Months Ended

Dec. 31, 2018

Stock-Based Awards

Stock-Based Awards

11. Stock-Based Awards

2014 Stock Incentive Plan

The 2014 Plan provides for the grant of incentive stock options, non-statutory stock options, restricted stock awards, restricted stock units, stock appreciation rights and other stock-based awards. The number of shares initially reserved for issuance under the 2014 Plan was 1,336,907 shares of common stock, which was increased to 2,126,907 on January 1, 2015. The number of shares reserved for issuance may be increased by the number of shares under the 2006 Stock Option Plan (the “2006 Plan”) that expire, terminate or are otherwise surrendered, cancelled, forfeited or repurchased by the Company. The number of shares of common stock that may be issued under the 2014 Plan is subject to increase on the first day of each fiscal year, beginning on January 1, 2015 and ending on December 31, 2024, equal to the least of 1,659,218 shares of the Company’s common stock, 4% of the number of shares of the Company’s common stock outstanding on the first day of the applicable fiscal year, and an amount determined by the Company’s board of directors. On January 1, 2018, the number of shares available for issuance under the 2014 Plan increased by 1,186,328. As of December 31, 2018, 1,581,243 shares remained available for issuance under the 2014 Plan.

As required by the 2006 Plan and 2014 Plan, the exercise price for stock options granted is not to be less than the fair value of common shares as of the date of grant. Prior to the IPO, the value of common stock was determined by the board of directors by taking into consideration its most recently available valuation of common shares performed by management and the board of directors as well as additional factors which might have changed since the date of the most recent contemporaneous valuation through the date of grant.

Inducement Stock Option Awards

On June 20, 2017, the Company issued to Antony Mattessich, who became a director of the Company on June 20, 2017 and the Company’s President and Chief Executive Officer on July 26, 2017, a non-statutory stock option to purchase an aggregate of 590,000 shares of the Company’s common stock at an exercise price of $10.94 per share. Subject to Mr. Mattessich’s continued service to the Company, the stock option will vest over a four-year period, with 25% of the shares underlying the option award vesting on the one year anniversary of the grant date and the remaining 75% of the shares underlying the award vesting monthly thereafter. The stock option was issued outside of the Company’s 2014 Stock Incentive Plan as an inducement material to Mr. Mattessich’s acceptance of entering into employment with the Company in accordance with Nasdaq Listing Rule 5635(c)(4).

2014 Employee Stock Purchase Plan

The Company’s has a 2014 Employee Stock Purchase Plan (the “ESPP”) with a total of 207,402 shares of common stock reserved for issuance under this plan which increased to 232,402 shares of common stock on January 1, 2015. The number of shares of common stock that may be issued under the ESPP will automatically increase on the first day of each fiscal year, commencing on January 1, 2015 and ending on December 31, 2024, in an amount equal to the least of 207,402 shares of the Company’s common stock, 0.5% of the number of shares of the Company’s common stock outstanding on the first day of the applicable fiscal year, and an amount determined by the Company’s board of directors. On January 1, 2018, the number of shares available for issuance under the 2014 Plan increased by 148,291. As of December 31, 2018, 401,510 shares of common stock remain available for issuance.

Stock Option Valuation

The fair value of each stock option grant is estimated on the date of grant using the Black-Scholes option-pricing model. The Company estimates its expected stock volatility based on the historical volatility of a publicly traded set of peer companies and expects to continue to do so until such time as it has adequate historical data regarding the volatility of its own traded stock price. Beginning in 2016, the Company estimates its expected volatility using a weighted average of the historical volatility of its publicly traded peer companies and the volatility of its common stock, and expect to continue to do so until such time as the Company has adequate historical data regarding the volatility of its traded stock price. The expected term of the Company’s stock options to employees has been determined utilizing the “simplified” method for awards that qualify as “plain-vanilla” options. The expected term of stock options granted to nonemployees is equal to the contractual term of the option award. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. Expected dividend yield is based on the fact that the Company has never paid cash dividends and does not expect to pay any cash dividends in the foreseeable future.

As of December 31, 2018, there were outstanding unvested service-based stock options held by nonemployees for the purchase of 7,917 shares of common stock.

The assumptions that the Company used to determine the fair value of the stock options granted to employees and directors are as follows, presented on a weighted average basis:


	Year Ended
	December 31,
	2018		2017		2016
Risk-free interest rate	2.65	%	2.00	%	1.42	%
Expected term (in years)	6		6		6
Expected volatility	102	%	102	%	85	%
Expected dividend yield	—	%	—	%	—	%

The following table summarizes the Company’s stock option activity:


				Weighted
		Weighted		Average
		Average		Remaining	Aggregate
	Shares Issuable	Exercise		Contractual	Intrinsic
	Under Options	Price		Term	Value
				(In years)
Outstanding as of December 31, 2017	4,002,374	$	10.08	7.2	$	1,222
Granted	1,883,157		5.59
Exercised	(182,261)		2.18
Forfeited	(472,439)		10.83
Outstanding as of December 31, 2018	5,230,831	$	8.67	7.5	$	654
Options vested and expected to vest as of December 31, 2018	4,954,183	$	8.82	7.4	$	654
Options exercisable as of December 31, 2018	2,629,571	$	10.57	6.2	$	654

The aggregate intrinsic value of stock options is calculated as the difference between the exercise price of the stock options and the fair value of the Company’s common stock for those stock options that had exercise prices lower than the fair value of the Company’s common stock. The aggregate intrinsic value of stock options exercised was $551, $408 and $575 during the years ended December 31, 2018, 2017 and 2016, respectively.

The weighted average grant date fair value of stock options granted to employees and directors during the years ended December 31, 2018, 2017, 2016 was $4.48, $6.44 and $4.52 per share, respectively.

Restricted Common Stock

The 2006 and 2014 Plans provide for the award of restricted common stock. The Company has granted restricted common stock with time-based vesting conditions. Unvested shares of restricted common stock may not be sold or transferred by the holder. These restrictions lapse according to the time-based vesting conditions of each award.

The aggregate intrinsic value of restricted stock awards is calculated as the positive difference between the prices paid, if any, of the restricted stock awards and the fair value of the Company’s common stock. There was no aggregate intrinsic value of restricted stock awards that vested during the years ended December 31, 2018, 2017 and 2016 and there was no remaining restricted shares at December 31, 2018 and 2017.

Stock-based Compensation

The Company recorded stock-based compensation expense related to stock options, vesting of restricted common stock and grants of common stock in the following expense categories of its statements of operations:


	Year Ended December 31,

	2018		2017		2016
Research and development	$	2,557	$	2,584	$	1,900
Selling and marketing		449		633		490
General and administrative		4,477		4,104		3,566
	$	7,483	$	7,321	$	5,956

As of December 31, 2018, the Company had an aggregate of $11,486 of unrecognized stock-based compensation cost, which is expected to be recognized over a weighted average period of 2.5 years.

Net Loss Per Share

12 Months Ended

Dec. 31, 2018

Net Loss Per Share

Net Loss Per Share

12. Net Loss Per Share

Basic and diluted net loss per share attributable to common stockholders was calculated as follows for the years ended December 31, 2018, 2017 and 2016:


	Year Ended December 31,
	2018		2017		2016
Numerator:
Net loss attributable to common stockholders	$	(59,978)	$	(63,386)	$	(44,703)
Denominator:
Weighted average common shares outstanding, basic and diluted		38,115,142		28,818,196		24,816,348
Net loss per share attributable to common stockholders, basic and diluted	$	(1.57)	$	(2.20)	$	(1.80)

The Company excluded the following common stock equivalents, outstanding as of December 31, 2018, 2017, and 2016, from the computation of diluted net loss per share attributable to common stockholders for the years ended December 31, 2018, 2017 and 2016 because they had an anti-dilutive impact due to the net loss incurred for the periods.


	December 31,
	2018	2017	2016
Options to purchase common stock	5,230,831	4,002,374	3,091,480
Warrants for the purchase of common stock	18,939	18,939	18,939
	5,249,770	4,021,313	3,110,419

Commitments and Contingencies

12 Months Ended

Dec. 31, 2018

Commitments and Contingencies.

Commitments and Contingencies

13. Commitments and Contingencies

Leases

The Company leases office, laboratory and manufacturing space in Bedford, Massachusetts and certain office equipment under non-cancelable operating leases that expire in July 2023 and July 2027.

Future minimum lease payments for its operating leases as of December 31, 2018 are as follows:


Year Ending December 31,
2019		1,809
2020		1,850
2021		1,886
2022		1,936
2023		1,730
Thereafter		5,224
Total	$	14,435

In October 2017, the Company and CCC Investors LLC (the “Landlord”) entered into an amendment (the “Second Amendment”) to a lease agreement for the Company’s laboratory and manufacturing space located at 34 Crosby Drive and 36 Crosby Drive, each in Bedford, Massachusetts. The Second Amendment amends the original lease agreement and extends the term of the Lease for 36 Crosby Drive from June 30, 2018 to July 31, 2023. Further, the Second Amendment acknowledges that the Company has previously vacated and surrendered, and the Lease has expired with regards to, 34 Crosby Drive, which reduces the Company’s required security deposit under the Lease from $228 to $114. Under the Second Amendment, the annual base rent for 36 Crosby Drive shall be approximately $524 until June 30, 2018, was $0 from July 1, 2018 to July 31, 2018, and shall be approximately $544 from August 1, 2018 to July 31, 2019. The annual base rent shall increase annually thereafter. The Second Amendment also provides the Company a one-time option to terminate the Lease on July 31, 2021, upon the Company’s delivery to the Landlord on or before July 31, 2020 of a termination notice and the payment to the Landlord of a termination fee of approximately $273.

In June 2016, the Company entered into a lease agreement for approximately 70,712 square feet of general office, research and development and manufacturing space in Bedford, Massachusetts. The lease term commenced on February 1, 2017 and will expire on July 31, 2027. The Company relocated its corporate headquarters to the new leased premises during June 2017 and is evaluating the potential relocation of its manufacturing operations to the new leased premises. No base rent was due under the lease until August 1, 2017. The initial annual base rent is approximately $1,200 and will increase annually beginning on February 1 of each year. The Company is obligated to pay all real estate taxes and costs related to the premises, including costs of operations, maintenance, repair, and replacement and management of the new leased premises. The Company posted a customary letter of credit in the amount of approximately $1,500 as a security deposit. The lease agreement allows for a landlord provided construction allowance not to exceed approximately $2,800 to be applied to the total construction costs of the new leased premises. The construction allowance was to be used on or before December 31, 2017, or it would be deemed forfeited with no further obligation by the landlord of the new leased premises. As of December 31, 2017, the Company has billed the landlord for $2,725 and received payments of $2,656 from the landlord. The Company forfeited $0.1 million under the construction allowance. Build out costs being reimbursed under the tenant improvement allowance have been recorded as deferred rent and will be amortized as a deduction to rent expense over the lease term.

The Company recognizes rent expense on a straight-line basis over the lease period and has recorded deferred rent for rent expense incurred but not yet paid. During the years ended December 31, 2018, 2017 and 2016, the Company recognized $1,788, $1,733 and $1,084, respectively, of rental expense, related to its office, laboratory and manufacturing space and office equipment.

Intellectual Property Licenses

The Company has a license agreement with Incept, LLC (“Incept”) (Note 16) to use and develop certain patent rights (the “Incept License”). Under the Incept License, as amended and restated, the Company was granted a worldwide, perpetual, exclusive license to develop and commercialize products that are delivered to or around the human eye for diagnostic, therapeutic or prophylactic purposes relating to ophthalmic diseases or conditions. The Company is obligated to pay low single-digit royalties on net sales of commercial products developed using the licensed technology, commencing with the date of the first commercial sale of such products and until the expiration of the last to expire of the patents covered by the license. Any of the Company’s sublicensees also will be obligated to pay Incept a royalty equal to a low single-digit percentage of net sales made by it and will be bound by the terms of the agreement to the same extent as the Company. The Company is obligated to reimburse Incept for its share of the reasonable fees and costs incurred by Incept in connection with the prosecution of the patent applications licensed to the Company under the Incept License. Through December 31, 2018, royalties paid under this agreement related to product sales were $214.

On September 13, 2018, (the “Effective Date) the Company entered into a second amended and restated license agreement (the “Second Amended Agreement”) with Incept. The Second Amended Agreement amends and restates in full the Company’s prior amended and restated Incept License (the “Prior Agreement” or “Original License”) to expand the scope of the Company’s intellectual property license and modify future intellectual property ownership and other rights thereunder.

Indemnification Agreements

In the ordinary course of business, the Company may provide indemnification of varying scope and terms to vendors, lessors, business partners, and other parties with respect to certain matters including, but not limited to, losses arising out of breach of such agreements or from intellectual property infringement claims made by third parties. In addition, the Company has entered into indemnification agreements with members of its board of directors and senior management team that will require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors or officers. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is, in many cases, unlimited. To date, the Company has not incurred any material costs as a result of such indemnifications. The Company does not believe that the outcome of any claims under indemnification arrangements will have a material effect on its financial position, results of operations or cash flows, and it has not accrued any liabilities related to such obligations in its consolidated financial statements as of December 31, 2018.

Purchase Commitments

Purchase commitments represent non-cancelable contractual commitments associated with certain clinical trial activities within the Company’s clinical research organization.

Manufacturing Commitments

Manufacturing contracts generally provide for termination on notice, and therefore are cancelable contracts but are contracts that the Company is likely to continue, regardless of the fact that they are cancelable.

Collaboration Agreement

On October 10, 2016, the Company entered into a Collaboration Agreement with Regeneron (Note 6). If the Option to enter into an exclusive worldwide license is exercised, Regeneron will conduct further preclinical development and an initial clinical trial under a collaboration plan. The Company is obligated to reimburse Regeneron for certain development costs incurred by Regeneron under the collaboration plan during the period through the completion of the initial clinical trial, subject to a cap of $25,000, which cap may be increased by up to $5,000 under certain circumstances, the timing of such payments are not known. If Regeneron elects to proceed with further development following the completion of the collaboration plan, it will be solely responsible for conducting and funding further development and commercialization of product candidates. If the Option is exercised, Regeneron is required to use commercially reasonable efforts to research, develop and commercialize at least one Licensed Product. Such efforts shall include initiating the dosing phase of a subsequent clinical trial within specified time periods following the completion of the first-in-human clinical trial or the initiation of preclinical toxicology studies, subject to certain extensions. Through December 31, 2018, the Option has not been exercised and no payments have been made to Regeneron.

Legal Proceedings

Securities Class Actions

On July 7, 2017, a putative class action lawsuit was filed against the Company and certain of the Company’s current and former executive officers in the United States District Court for the District of New Jersey, captioned Thomas Gallagher v. Ocular Therapeutix, Inc, et al., Case No. 2:17-cv-05011. The complaint purports to be brought on behalf of shareholders who purchased the Company’s common stock between May 5, 2017 and July 6, 2017. The complaint generally alleges that the Company and certain of the Company’s current and former officers violated Sections 10(b) and/or 20(a) of the Securities Exchange Act of 1934 (“Exchange Act”) and Rule 10b-5 promulgated thereunder by making allegedly false and/or misleading statements concerning the Form 483 issued by the FDA related to DEXTENZA and the Company’s manufacturing operations for DEXTENZA. The complaint seeks unspecified damages, attorneys’ fees, and other costs. On July 14, 2017, an amended complaint was filed; the amended complaint purports to be brought on behalf of shareholders who purchased the Company’s common stock between May 5, 2017 and July 11, 2017, and otherwise includes allegations similar to those made in the original complaint.

On July 12, 2017, a second putative class action lawsuit was filed against the Company and certain of the Company’s current and former executive officers in the United States District Court for the District of New Jersey, captioned Dylan Caraker v. Ocular Therapeutix, Inc., et al., Case No. 2:17-cv-05095. The complaint purports to be brought on behalf of shareholders who purchased the Company’s common stock between May 5, 2017 and July 6, 2017. The complaint includes allegations similar to those made in the Gallagher complaint, and seeks similar relief.

On August 3, 2017, a third putative class action lawsuit was filed against the Company and certain of the Company’s current and former executive officers in the United States District Court for the District of New Jersey, captioned Shawna Kim v. Ocular Therapeutix, Inc., et al., Case No. 2:17-cv-05704. The complaint purports to be brought on behalf of shareholders who purchased the Company’s common stock between March 10, 2016 and July 11, 2017. The complaint includes allegations similar to those made in the Gallagher complaint, and seeks similar relief.

On October 27, 2017, a magistrate judge for the United States District Court for the District of New Jersey granted the defendants’ motion to transfer the above-referenced Gallagher, Caraker, and Kim litigations to the United States District Court for the District of Massachusetts. These matters were assigned the following docket numbers in the District of Massachusetts: 1:17-cv-12288 (Gallagher), 1:17-cv-12146 (Caraker), and 1:17-cv-12286 (Kim).

On March 9, 2018, the court consolidated the three actions and appointed co-lead plaintiffs and co-lead counsel for the consolidated action. On May 7, 2018, co-lead plaintiffs filed a consolidated amended class action complaint. The amended complaint makes allegations similar to those in the original complaints, against the same defendants, and seeks similar relief on behalf of shareholders who purchased the Company’s common stock between March 10, 2016 and July 11, 2017. The amended complaint generally alleges that defendants violated Sections 10(b) and/or 20(a) of the Exchange Act and Rule 10b-5 promulgated thereunder. On July 6, 2018, defendants filed a motion to dismiss the consolidated amended complaint. Plaintiffs’ filed an opposition to the motion to dismiss on September 4, 2018, and defendants filed a reply on October 4, 2018. The court held oral argument on the motion to dismiss on February 6, 2019 and took the matter under advisement.

The Company denies any allegations of wrongdoing and intends to vigorously defend against these lawsuits.

Shareholder Derivative Litigation

On July 11, 2017, a purported shareholder derivative lawsuit was filed against certain of the Company’s current and former executive officers, certain current and former board members, and the Company as a nominal defendant, in the United States District Court for the District of Massachusetts, captioned Robert Corwin v. Sawhney et al., Case No. 1:17-cv-11270. The complaint generally alleged that the individual defendants breached fiduciary duties owed to the Company by making allegedly false and/or misleading statements concerning the Form 483 related to DEXTENZA and our manufacturing operations for DEXTENZA. The complaint purported to assert claims against the individual defendants for breach of fiduciary duty, and sought to recover on behalf of the Company for any liability the Company incurs as a result of the individual defendants’ alleged misconduct. The complaint also sought contribution on behalf of the Company from all individual defendants for their alleged violations of Sections 10(b) and/or 20(a) of the Exchange Act and Rule 10b-5 promulgated thereunder. The complaint sought declaratory, equitable, and monetary relief, an unspecified amount of damages, with interest, and attorneys’ fees and costs. On September 20, 2017, counsel for the plaintiff filed a notice of voluntary dismissal, stating that the plaintiff wished to coordinate his efforts and proceed in a consolidated fashion with the plaintiff in a similar derivative suit that was pending in the Superior Court of Suffolk County of the Commonwealth of Massachusetts captioned Angel Madera v. Sawhney et al., Case. No. 17-2273 (which is discussed in the paragraph immediately below) by filing an action in that court subsequent to the dismissal of this lawsuit. The Corwin lawsuit was dismissed without prejudice on September 21, 2017. On October 24, 2017, the plaintiff filed a new derivative complaint in Massachusetts Superior Court (Suffolk County), captioned Robert Corwin v. Sawhney et al., Case No. 17-3425 (BLS2). The new Corwin complaint includes allegations similar to those made in the federal court complaint and asserts a derivative claim for breach of fiduciary duty against certain of our current and former officers and directors. The complaint also asserts an unjust enrichment claim against two additional defendants, SV Life Sciences Fund IV, LP and SV Life Sciences Fund IV Strategic Partners, LP. The complaint also names the Company as a nominal defendant.

On July 19, 2017, a second purported shareholder derivative lawsuit was filed against certain of the Company’s current and former executive officers, all current board members, one former board member, and the Company as a nominal defendant, in the Superior Court of Suffolk County of the Commonwealth of Massachusetts, captioned Angel Madera v. Sawhney et al., Case. No. 17-2273. The complaint included allegations similar to those made in the Corwin complaint. The complaint purported to assert derivative claims against the individual defendants for breach of fiduciary duty, unjust enrichment, abuse of control, gross mismanagement, and waste of corporate assets, and sought to recover on behalf of the Company for any liability the Company incurs as a result of the individual defendants’ alleged misconduct. The complaint sought declaratory, equitable, and monetary relief, an unspecified amount of damages, with interest, and attorneys’ fees and costs. On November 6, 2017, the court dismissed this action without prejudice due to plaintiff’s failure to complete service of process within the time permitted under applicable court rules. On December 21, 2017, the same plaintiff filed a new derivative complaint in the same court, captioned Angel Madera v. Sawhney et al., Case. No. 17-4126 (BLS2). The new Madera complaint is premised on substantially similar allegations as the previous complaint and purports to assert derivative claims against certain current and former executive officers and board members for breach of fiduciary duty, unjust enrichment, and waste of corporate assets, and names the Company as a nominal defendant. Like the new Corwin complaint, the new Madera complaint also asserts an unjust enrichment claim against two additional defendants, SV Life Sciences Fund IV, LP and SV Life Sciences Fund IV Strategic Partners, LP.

By order dated January 29, 2018, the court consolidated the state court Corwin and Madera complaints under the Corwin docket and appointed lead counsel for plaintiffs. On February 28, 2018, plaintiffs filed a consolidated amended complaint. The consolidated complaint names substantially the same defendants and is premised on substantially similar allegations as the previous Corwin and Madera complaints, asserting claims for breach of fiduciary duty against the individual defendants and unjust enrichment against the two SV entity defendants. On April 17, 2018, all defendants served a motion to dismiss the consolidated amended complaint. On June 22, 2018, plaintiffs served their opposition to the motion to dismiss and a cross-motion to stay the proceedings pending a decision on the motion to dismiss in the above-referenced securities class action in the District of Massachusetts. On July 30, 2018, the parties filed a joint motion to stay the proceedings pending a decision on the motion to dismiss in the above-referenced securities class action in the District of Massachusetts. On August 3, 2018, the court granted the motion to stay.

On January 31, 2018, a third purported shareholder derivative suit was filed against certain of the Company’s current and former executive officers, certain current and former board members, and the Company as a nominal defendant, in the United States District Court for the District of Massachusetts, captioned Brian Robinson v. Sawhney et al., Case. No. 1:18-cv-10199. The complaint includes allegations similar to those made in the Corwin and Madera complaints. The complaint does not name either SV Life Sciences Fund, IV, LP or SV Life Sciences Fund IV Strategic Partners, LP as defendants, and adds two former officers as defendants. The complaint purports to assert derivative claims against the individual defendants for breach of fiduciary duty, waste of corporate assets, and unjust enrichment, and seeks to recover on behalf of the Company for any liability the Company incurs as a result of the individual defendants’ alleged misconduct. The complaint seeks declaratory, equitable, and monetary relief, an unspecified amount of damages, with interest, and attorneys’ fees and costs. On April 30, 2018, all defendants filed a motion to dismiss or stay the complaint. Plaintiff filed his opposition on June 22, 2018. On July 26, 2018, the parties filed a joint motion to extend the deadline for defendants to file their reply brief pending the potential substitution of the named shareholder plaintiff. On August 20, 2018, the parties filed a joint stipulation and proposed order regarding plaintiff’s unopposed request to substitute a new shareholder plaintiff and the parties’ joint request that the court stay the proceedings pending a decision on the motion to dismiss in the above-referenced securities class action in the District of Massachusetts. On September 4, 2018, the court entered the requested order substituting the named plaintiff and staying the matter.

On February 16, 2018, a fourth purported shareholder derivative suit was filed against certain of the Company’s current and former executive officers, certain current and former board members, and the Company as a nominal defendant, in the United States District Court for the District of Delaware, captioned Terry Kelly v. Sawhney et al., Case. No. 1:18-cv-00277. The complaint includes allegations similar to those made in the Corwin and Madera complaints. The complaint purports to assert derivative claims against the individual defendants for breach of fiduciary duty, unjust enrichment and waste of corporate assets, and seeks to recover on behalf of the Company for any liability the Company incurs as a result of the individual defendants’ alleged misconduct. The complaint also asserts an unjust enrichment claim against SV Life Sciences Fund IV, LP and SV Life Sciences Fund IV Strategic Partners, LP. The complaint seeks declaratory, equitable, and monetary relief, an unspecified amount of damages, with interest, and attorneys’ fees and costs. On June 11, 2018, the parties filed a stipulation staying the lawsuit pending final judgment in the consolidated derivative action pending in Massachusetts state court under the Corwin docket, described above. The court entered an order staying the case on June 12, 2018.

The Company denies any allegations of wrongdoing and intend to vigorously defend against these lawsuits.

In addition, the Company has received a subpoena from the SEC, dated December 15, 2017, requesting documents and information concerning DEXTENZA (dexamethasone insert) 0.4mg, including related communications with the FDA, investors and others. The Company received a second subpoena from the SEC on August 21, 2018, requesting documents and information concerning its participation in two investor conferences in June 2017. The Company intends to fully cooperate with the SEC regarding this non-public, fact-finding inquiry. The SEC has informed the Company that this inquiry should not be construed as an indication that any violations of law have occurred or that the SEC has any negative opinion of any person, entity or security.

The Company is unable to predict the outcome of these lawsuits or proceedings at this time. Moreover, any conclusion of these matters in a manner adverse to the Company and for which it incurs substantial costs or damages not covered by our directors’ and officers’ liability insurance would have a material adverse effect on the Company’s financial condition and business. In addition, the proceedings could adversely impact the Company’s reputation and divert management’s attention and resources from other priorities, including the execution of business plans and strategies that are important to the Company’s ability to grow the Company’s business, any of which could have a material adverse effect on the Company’s business.

Income Taxes

12 Months Ended

Dec. 31, 2018

Income Taxes

Income Taxes

14. Income Taxes

2017 U.S. Tax Reform

On December 22, 2017 President Trump signed into law the “Tax Cuts and Jobs Act” (“TCJA”) that significantly reforms the Internal Revenue Code of 1986, as amended. The TCJA, among other things, contains significant changes to corporate taxation, including reduction of the corporate tax rate from a top marginal rate of 35% to a flat rate of 21% effective as of January 1, 2018. Additionally, the TCJA contained provisions for the limitation of the tax deduction for interest expense; limitation of the deduction for net operating losses to 80% of current year taxable income and elimination of net operating loss carrybacks in each case for losses arising in taxable years beginning after December 31, 2017(though any such tax losses may be carried forward indefinitely); and modifying or repealing many business deductions and credits. This includes reducing the business tax credit for certain clinical testing expenses incurred in the testing of certain drugs for rare disease or conditions generally referred to as ‘orphan drugs’.

The staff of the Securities and Exchange Commission issued Staff Accounting Bulletin No. 118 to address the application of U.S. GAAP in situations when a registrant does not have the necessary information available, prepared or analyzed (including computations) in reasonable detail to complete the accounting for certain income tax effects of the TCJA. In connection with the initial analysis of the impact of the TCJA, the Company remeasured its deferred tax assets and liabilities based on the rates at which they are expected to reverse in the future, which is generally 21%. The remeasurement of the Company’s deferred tax assets and liabilities was offset by a corresponding change in the valuation allowance for the year ended December 31, 2017. As a result, there was no impact to the Company’s consolidated statements of operations and comprehensive loss as a result of the reduction in tax rates. The other provisions of the TCJA did not have a material impact on the Company’s consolidated financial statements. The Company’s final determination of the TCJA impact and the remeasurement of its deferred assets and liabilities was completed prior to the deadline of one year from the enactment of the TCJA. For the year ended December 31, 2018, there were no material changes to the analysis originally performed as of December 31, 2017.

Income Taxes

During the years ended December 31, 2018, 2017 and 2016, the Company recorded no income tax benefits for the net operating losses incurred or the research and development tax credits generated in each year, due to its uncertainty of realizing a benefit from those items.

A reconciliation of the U.S. federal statutory income tax rate to the Company’s effective income tax rate is as follows:


	Year Ended December 31,
	2018		2017		2016
Federal statutory income tax rate	(21.0)	%	(34.0)	%	(34.0)	%
Tax reform change	—		43.0		—
Research and development tax credits	(3.6)		(3.3)		(2.9)
State taxes, net of federal benefit	(4.5)		(3.8)		(4.8)
Stock-based compensation	1.3		2.2		1.4
Other	0.1		(0.2)		(0.6)
Change in deferred tax asset valuation allowance	27.7		(3.9)		40.9
Effective income tax rate	—	%	—	%	—	%

Net deferred tax assets consisted of the following:


	December 31,
	2018		2017
Net operating loss carryforwards	$	49,699	$	33,094
Tax credit carryforwards		10,160		7,971
Capitalized start-up costs		870		1,022
Capitalized research and development expenses, net		18,418		21,869
Accrued expenses and other temporary differences		5,196		3,770
Total gross deferred tax assets		84,343		67,726
Valuation allowance		(84,343)		(67,726)
Net deferred tax assets	$	—	$	—

Changes in the valuation allowance for deferred tax assets during the years ended December 31, 2018, 2017 and 2016 related primarily to the increase in net operating loss carryforwards, capitalized research and development expenses and research and development tax credit carryforwards offset in 2017 by a decrease in a deferred tax asset resulting from the decreased federal corporate tax rate and were as follows:


	Year Ended December 31,
	2018		2017		2016
Valuation allowance as of beginning of year	$	67,726	$	70,236	$	51,969
Increases recorded to income tax provision		16,617		24,773		18,267
Decreases recorded to income tax provision		—		(27,283)		—
Valuation allowance as of end of year	$	84,343	$	67,726	$	70,236

As of December 31, 2018, the Company had net operating loss carryforwards for federal and state income tax purposes of $190,555 and $161,837, respectively. The federal and state net operating losses generated for annual periods prior to January 1, 2018 begin to expire in 2026. The Company’s federal net operating losses generated for the year ended December 31, 2018, which amounted to $64,327, can be carried forward indefinitely. As of December 31, 2018, the Company also had available research and development tax credit carryforwards for federal and state income tax purposes of $7,036 and $3,611, respectively, which begin to expire in 2026 and 2025, respectively. Utilization of the net operating loss carryforwards and research and development tax credit carryforwards may be subject to a substantial annual limitation under Section 382 of the Internal Revenue Code of 1986 due to ownership changes that have occurred previously or that could occur in the future. These ownership changes may limit the amount of carryforwards that can be utilized annually to offset future taxable income. In general, an ownership change, as defined by Section 382, results from transactions increasing the ownership of certain shareholders or public groups in the stock of a corporation by more than 50% over a three-year period. The Company has not conducted a study to assess whether a change of control has occurred or whether there have been multiple changes of control since inception due to the significant complexity and cost associated with such a study. If the Company has experienced a change of control, as defined by Section 382, at any time since inception, utilization of the net operating loss carryforwards or research and development tax credit carryforwards would be subject to an annual limitation under Section 382, which is determined by first multiplying the value of the Company’s stock at the time of the ownership change by the applicable long-term tax-exempt rate, and then could be subject to additional adjustments, as required. Any limitation may result in expiration of a portion of the net operating loss carryforwards or research and development tax credit carryforwards before utilization. Further, until a study is completed and any limitation is known, no amounts are being presented as an uncertain tax position.

The Company has evaluated the positive and negative evidence bearing upon its ability to realize the deferred tax assets. Management considered the Company’s cumulative net losses and concluded that it is more likely than not that the Company would not realize the benefits of the deferred tax assets. Accordingly, a full valuation allowance was established against the net deferred tax assets as of December 31, 2018 and 2017. The valuation allowance increased by approximately $16,617 in 2018 as a result of the increase in deferred tax assets primarily related to net operating loss carryforwards. In 2017, the valuation allowance, on a net basis, decreased by approximately $2,510 due to the decrease in corporate tax rate offset by an increase in deferred tax assets related to net operating loss carryforwards.

The Company has not recorded any amounts for unrecognized tax benefits as of December 31, 2018 or 2017.

The Company files tax returns as prescribed by the tax laws of the jurisdictions in which it operates. In the normal course of business, the Company is subject to examination by federal and state jurisdictions, where applicable. There are currently no pending income tax examinations. The Company’s tax years are still open under statute from December 31, 2015 to the present. Earlier years may be examined to the extent that tax credit or net operating loss carryforwards are used in future periods. The Company’s policy is to record interest and penalties related to income taxes as part of its income tax provision. As of December 31, 2018 and 2017, the Company had no accrued interest or penalties related to uncertain tax positions and no amounts have been recognized in the Company’s statements of operations and comprehensive loss.

401(k) Savings Plan	12 Months Ended
401(k) Savings Plan	Dec. 31, 2018
401(k) Savings Plan
401(k) Savings Plan	15. 401(k) Savings Plan The Company established a defined contribution savings plan under Section 401(k) of the Internal Revenue Code. This plan covers substantially all employees who meet minimum age and service requirements and allows participants to defer a portion of their annual compensation on a pre-tax basis. Company contributions to the plan may be made at the discretion of the board of directors. Through December 31, 2018, no contributions have been made to the plan by the Company.

Related Party Transactions	12 Months Ended
Related Party Transactions	Dec. 31, 2018
Related Party Transactions
Related Party Transactions	16. Related Party Transactions The Company has a license agreement with Incept to use and develop certain patent rights that it entered into in 2007. Royalties incurred and payable to Incept have not been material to date. The Company’s former President and Chief Executive Officer and current Executive Chairman and Chairman of the Company’s board of directors is a general partner of Incept. Since October 2017, the Company has engaged McCarter English LLP (“McCarter”) to provide legal services to the Company, including with respect to intellectual property matters. The Company’s Senior Vice President, Technical Operations, Kevin Hanley, who joined the Company in January 2018, is married to a partner at McCarter, who has not participated in providing legal services to the Company. The Company incurred fees for legal services rendered by McCarter of $1,019 and $42 for the year ended December 31, 2018 and 2017, respectively. As of December 31, 2018, there was $526 recorded in accounts payable for McCarter. In March 2016, the Company entered into a Master Services Agreement with Axtria, Inc. (“Axtria”). In March 2016, the Company entered into a statement of work totaling approximately $104 under which Axtria would provide certain sales and marketing analytics to the Company. In February 2017, the Company entered into a separate statement of work totaling approximately $1,400 under which Axtria would provide data warehouse implementation, operations and maintenance support services to the Company. Jaswinder Chadha, co-founder and CEO of Axtria, is also a member of the Company’s Board of Directors and a cousin to the Company’s Executive Chairman of the Board of Directors and former President and Chief Executive Officer. For the years ended December 31, 2017 and 2016, payments paid to Axtria were $864 under the 2017 statement of work and $150 under the 2016 statement of work, respectively. As of December 31, 2017, there were no amounts due in accounts payable to Axtria. On July 20, 2017, the Company terminated the 2017 and 2016 statements of work with Axtria. Since 2014, the Company has engaged Wilmer Cutler Pickering Hale and Dorr LLP (“WilmerHale”) to provide legal services to the Company, including with respect to general corporate, finance, securities law, regulatory and licensing matters. The Company’s former Chief Medical Officer, Jonathan H. Talamo, M.D., who served as Chief Medical Officer from July 2016 until his resignation in June 2017, is married to a partner at WilmerHale, who has not participated in providing legal services to the Company. The Company incurred fees for legal services rendered by WilmerHale of $1,368 and $874 for the year ended December 31, 2017 and 2016, respectively. As of December 31, 2017, there was $194, recorded in accounts payable for WilmerHale. As of December 31, 2017, there was $80, recorded in accrued expenses for WilmerHale.

Restructuring and Other Costs

12 Months Ended

Dec. 31, 2018

Restructuring and Other Costs

Restructuring and Other Costs

17. Restructuring and Other Costs

On July 31, 2017, the Board of Directors approved a strategic restructuring to eliminate a portion of the Company’s workforce as part of an initiative to enhance operations and reduce expenses. As part of this strategic restructuring, the Company eliminated 30 positions across the organization. During the twelve months ended December 31, 2017, the Company recorded $1,703 of restructuring-related costs in operating expenses in research and development and selling and marking, including employee severance, benefits and related costs.

On July 31, 2017, the Company entered into a transition, separation and release of claims agreement (the “Ankerud Transition Agreement”), pursuant to which Eric Ankerud resigned from his role as Executive Vice President, Regulatory, Quality and Compliance of the Company, effective immediately. Mr. Ankerud continued to serve as an at-will employee of the Company in the capacity of Senior Advisor until October 31, 2017. He currently serves as a consultant to the Company. Under the Ankerud Transition Agreement, Mr. Ankerud is entitled to separation benefits until October 31, 2018, in the form of continuation of his base salary in the same amount in effect as of October 31, 2018; the payment of monthly premiums for healthcare and/or dental coverage; and provided he continues to provide services to the Company as a consultant, the continued vesting of his outstanding stock options awards in accordance with the applicable equity plans and stock option agreements. During the twelve months ended December 31, 2017, the Company recorded $386 of severance expense which are included in operating expenses in research and development.

On October 13, 2017, the Company entered into a transition, separation and release of claims agreement (the “Fortune Transition Agreement”) with James Fortune, pursuant to which Mr. Fortune resigned from his role as Chief Operating Officer and any and all other positions he holds as an officer or employee of the Company, effective December 31, 2017 (the “Separation Date”). Pursuant to the Fortune Transition Agreement, effective as of October 13, 2017, the Employment Agreement, by and between the Company and Mr. Fortune, dated June 19, 2014, was terminated. Under the Fortune Transition Agreement, Mr. Fortune will be entitled to separation benefits in the form of (i) the continuation of his base salary for twelve months after the Separation Date in the same amount in effect as of the October 13, 2017 and (ii) the payment of monthly premiums for healthcare and/or dental coverage at the same rate that is in effect on the Separation Date until the earlier of twelve months from the Separation Date or the date Mr. Fortune becomes eligible to receive such benefits under another employer’s benefit plan. Should any annual bonus payments be made to active Company executives for the calendar year 2017, Mr. Fortune will also be eligible to receive a bonus payment in such amount, if any, he would have received had he remained employed with the Company through the date of such bonus payments. During the twelve months ended December 31, 2017, the Company recorded $417 of severance expense which are included in operating expenses in general and administration.

The following table summarizes the restructuring and other costs by category during the twelve months ended December 31, 2017:

wwe

	Twelve Months Ended December 31, 2017
	Total
Research and development	$	690
Selling and marketing		1,399
General and administration		417
	$	2,506

The following table summarizes the restructuring and other costs reserve for the periods indicated:


	Year Ended
	December 31, 2018
Restructuring and other costs at December 31, 2017	$	960
Amounts paid during the period		(960)
Restructuring and other costs at December 31, 2018	$	—

Selected Quarterly Financial Data (Unaudited)

12 Months Ended

Dec. 31, 2018

Selected Quarterly Financial Data (Unaudited)

Selected Quarterly Financial Data (Unaudited)

18. Selected Quarterly Financial Data (Unaudited)


	Three Months Ended
	Dec. 31,		Sept. 30,		June 30,		Mar 31,		Dec. 31,		Sept. 30,		June 30,		Mar 31,
	2018		2018		2018		2018		2017		2017		2017		2017
Statements of Operations Data:
Product revenue	$	504	$	498	$	648	$	340	$	487	$	523	$	438	$	475
Revenue		504		498		648		340		487		523		438		475
Loss from operations		(17,283)		(14,816)		(13,564)		(13,455)		(12,716)		(15,196)		(18,339)		(15,672)
Net loss		(17,399)		(15,010)		(13,804)		(13,765)		(13,102)		(15,567)		(18,694)		(16,023)
Basic and diluted net loss per common share	$	(0.42)	$	(0.38)	$	(0.37)	$	(0.40)	$	(0.44)	$	(0.54)	$	(0.64)	$	(0.58)

Subsequent Events	12 Months Ended
Subsequent Events	Dec. 31, 2018
Subsequent Events
Subsequent Events	19. Subsequent Events The number of shares of common stock that may be issued under the 2014 Plan is subject to increase on the first day of each fiscal year, beginning on January 1, 2015 and ending on December 31, 2024, equal to the least of 1,659,218 shares of the Company’s common stock, 4% of the number of shares of the Company’s common stock outstanding on the first day of the applicable fiscal year, and an amount determined by the Company’s board of directors. On January 1, 2019, the number of shares available for issuance under the 2014 Plan increased by 1,659,218. The number of shares of common stock that may be issued under the ESPP will automatically increase on the first day of each fiscal year, commencing on January 1, 2015 and ending on December 31, 2024, in an amount equal to the least of 207,402 shares of the Company’s common stock, 0.5% of the number of shares of the Company’s common stock outstanding on the first day of the applicable fiscal year, and an amount determined by the Company’s board of directors. On January 1, 2019, the number of shares available for issuance under the ESPP increased by 207,402. The Company sold an additional 1,318,481 shares of common stock between January 1, 2019 and February 22, 2019, at-the-market under the 2016 Sales Agreement discussed in Note 10, resulting in net proceeds of approximately $4,967 after underwriting discounts, commissions and expenses. As of February 25, 2019, the Company had nothing remaining available for future sale under the 2016 Sales Agreement. On February 28, 2019, pursuant to the 2016 Sales Agreement, the Company delivered a termination notice to Cantor, terminating the 2016 Sales Agreement. Private Placement of Convertible Debt In March 2019, the Company entered into a Note Purchase Agreement (the “Purchase Agreement”), with Cap 1 LLC, (the “Purchaser”) an affiliate of Summer Road LLC, to issue and sell to the Purchaser unsecured senior subordinated convertible notes, (“the Notes”), in the original aggregate principal amount of $37.5 million within five business days of the Agreement Date or upon such later date as mutually agreed between the Company and the Purchaser in writing (such date, the “Closing Date”). In accordance with the Purchase Agreement, each Note accrues interest at a rate of 6% of its outstanding principal amount per annum, payable at maturity. The maturity date of each Note is March 1, 2026, unless earlier converted, repurchased or redeemed as described below. Holders may, subject to certain conditions, convert all or part of the outstanding principal amount of their Notes into shares of the Company’s common stock, par value $0.0001 per share, or the Common Stock, provided that no conversion results in a holder beneficially owning more than 19.99% of the issued and outstanding Common Stock of the Company. The conversion rate for the Notes will initially be 153.8462 shares of the Company’s common stock per $1,000 principal amount of the Notes, which is equivalent to an initial conversion price of approximately $6.50 per share. The conversion rate is subject to adjustment in customary circumstances such as stock splits or similar changes to the Company’s capitalization. At its election, the Company may choose to make such conversion payment in cash, in shares of Common Stock, or in a combination thereof. Upon any conversion of any Note, the Company is obligated to make a cash payment to the holder of such Note for any interest accrued but unpaid on the principal amount converted. Upon the occurrence of a Corporate Transaction (as defined in the Notes), the holder of a Note is entitled, at such holder’s option, to convert all of the outstanding principal amount of the Note in accordance with the foregoing and receive an additional, “make-whole” cash payment in accordance with a table set forth in each Note. Upon the occurrence of a Corporate Transaction, each holder of a Note has the option to require the Company to repurchase all or part of the outstanding principal amount of such Note at a repurchase price equal to 100% of the outstanding principal amount of the Note to be repurchased, plus accrued and unpaid interest to, but excluding, the repurchase date. On or after March 1, 2022, if the last reported sale price of the Common Stock has been at least 130% of the conversion rate then in effect for twenty of the preceding thirty trading days (including the last trading day of such period), the Company is entitled, at its option, to redeem all or part of the outstanding principal amount of the Notes, on a pro rata basis, at an optional redemption price equal to 100% of the outstanding principal amount of the Notes to be redeemed, plus accrued and unpaid interest to, but excluding, the optional redemption date. The Purchase Agreement contains customary representations and warranties by the Company and the Purchaser. The Purchase Agreement does not include any financial covenants. The Company’s obligations under the Purchase Agreement and the Notes are subject to acceleration upon the occurrence of specified events of default, including a default or breach of certain contracts material to the Company and the delisting and deregistration of the Common Stock. In connection with the execution of the Purchase Agreement and the issuance and sale of the Notes thereunder, the Company and the Purchaser have agreed to enter into a registration rights agreement on the Closing Date, (the “Registration Rights Agreement”). Under the terms of the Registration Rights Agreement and subject to specified exceptions, the Company will be obligated to use commercially reasonable efforts, at its expense, to file a resale registration statement (the “Registration Statement”) with the SEC to register the Common Stock underlying the Notes within 30 days of the Closing Date and to have the SEC declare the Registration Statement effective within 90 days of the Closing Date. The Company will be further obligated to use commercially reasonable efforts to cause the Registration Statement to remain continuously effective until the earlier of the dates when all securities registrable under the Registration Rights Agreement (i) have been sold or (ii) may be sold without restriction, subject to certain conditions, pursuant to Rule 144 promulgated under the Securities Act of 1993, as amended. Amendment to Existing 2018 Amended Credit Facility In accordance with the 2018 Amended Credit Facility, in connection with the Company’s desire to enter into the Purchase Agreement and issue and sell the Notes thereunder, the Company, MidCap, and the Senior Lenders entered into an amendment to the 2018 Amended Credit Facility (“Subsequent Amendment”) on February 21, 2019 (the “Agreement Date”). The Subsequent Amendment added to the 2018 Amended Credit Facility, among other provisions, a negative covenant restricting the Company from paying the holders of the Notes ahead in priority to the Senior Lenders, for so long as indebtedness remains outstanding under the Credit Facility, and a cross-default provision to establish that an event of default under the Purchase Agreement also constituted an event of default under the Credit Agreement. Subordination Agreement In connection with the execution of the Subsequent Amendment, the Company; Cap 1, for itself and on behalf of any future holder of the Notes, or collectively, the Subordinated Creditors; and MidCap, as agent for the Senior Lenders, entered a subordination agreement on the Agreement Date (the “Subordination Agreement”). Under the terms of the Subordination Agreement, as an inducement to the Senior Lenders to permit the issuance and sale of the Notes, the Senior Lenders and the Subordinated Creditors agreed that the Notes are subordinate to the Credit Facility and that any and all payments to the holders of the Notes are subject to the payment in full of the Credit Facility. Until the Credit Facility is paid in full, as defined in the Subordination Agreement, the Subordinated Creditors agree not to take any enforcement action, as defined in the Subordination Agreement, with respect to all or any portion of the Notes, without the prior written consent of the agent for the Senior Lenders.

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2018

Summary of Significant Accounting Policies

Basis of Presentation and Principles of Consolidation

The accompanying consolidated financial statements reflect the operations of the Company and its wholly-owned subsidiary. All intercompany accounts and transactions have been eliminated.

Inventory is valued at the lower of cost or net realizable value, determined by the first-in, first-out (“FIFO”) method.

Inventory consisted of the following:


	December 31,
	2018		2017
Raw materials	$	112	$	68
Work-in-process		33		37
Finished goods		72		17
	$	217	$	122

Restricted Cash

Concentration of Credit Risk and of Significant Suppliers

Fair Value Measurements

Level 1—Quoted prices in active markets for identical assets or liabilities.

Property and Equipment

Impairment of Long-Lived Assets

Research and Development Costs

Research Contract Costs and Accruals

Patent Costs

Accounting for Stock-Based Compensation

Income Taxes

Segment Data

Comprehensive Loss

Net Income (Loss) Per Share

Deferred Offering Costs

Recently Issued and Adopted Accounting Pronouncements

Recently Adopted Accounting Pronouncements


	December 31,		December 31,		December 31,
	2018		2017		2016
Cash and cash equivalents	$	54,062	$	41,538	$	32,936
Restricted cash		6,614		1,614		1,728
Total cash, cash equivalents and restricted cash as shown on the statement of cash flow	$	60,676	$	43,152	$	34,664

Recently Issued Accounting Pronouncements

Summary of Significant Accounting Policies - (Tables)

12 Months Ended

Dec. 31, 2018

Summary of Significant Accounting Policies

Components of Inventory


	December 31,
	2018		2017
Raw materials	$	112	$	68
Work-in-process		33		37
Finished goods		72		17
	$	217	$	122

Reconciliation of cash, cash equivalents, and restricted cash reported within the balance sheet to the total amounts shown in the statement of cash flows


	December 31,		December 31,		December 31,
	2018		2017		2016
Cash and cash equivalents	$	54,062	$	41,538	$	32,936
Restricted cash		6,614		1,614		1,728
Total cash, cash equivalents and restricted cash as shown on the statement of cash flow	$	60,676	$	43,152	$	34,664

Fair Value of Financial Assets and Liabilities (Tables)

12 Months Ended

Dec. 31, 2018

Fair Value of Financial Assets and Liabilities

Schedule of Assets and Liabilities Measured at Fair Value on Recurring Basis


	Fair Value Measurements as of
	December 31, 2018 Using:
	Level 1		Level 2		Level 3		Total
Assets:
Cash equivalents:
Money market funds	$	—	$	50,906	$	—	$	50,906
Total	$	—	$	50,906	$	—	$	50,906


	Fair Value Measurements as of
	December 31, 2017 Using:
	Level 1		Level 2		Level 3		Total
Assets:
Cash equivalents:
Money market funds	$	—	$	40,386	$	—	$	40,386
Total	$	—	$	40,386	$	—	$	40,386

Property and Equipment, net (Tables)

12 Months Ended

Dec. 31, 2018

Property and Equipment, net

Schedule of Property and Equipment net


	December 31,
	2018		2017
Equipment	$	7,917	$	6,183
Leasehold improvements		8,675		8,553
Furniture and fixtures		760		740
Software		180		118
Construction in progress		331		225
		17,863		15,819
Less: Accumulated depreciation		(7,627)		(5,341)
	$	10,236	$	10,478

Accrued Expenses and Deferred Rent (Tables)

12 Months Ended

Dec. 31, 2018

Accrued Expenses and Deferred Rent

Schedule of Accrued Expenses


	December 31,		December 31,
	2018		2017
Accrued payroll and related expenses	$	3,558	$	2,936
Accrued rent		267		267
Accrued professional fees		1,393		534
Accrued research and development expenses		380		217
Accrued other		596		356
	$	6,194	$	4,310

Notes Payable (Tables)

12 Months Ended

Dec. 31, 2018

Notes Payable.

Schedule of borrowings outstandings


	December 31, 2018		December 31, 2017
Borrowings outstanding	$	25,000	$	18,000
Accrued exit fee		5		221
Unamortized discount		(217)		(205)
	$	24,788	$	18,016

Schedule of Annual Repayment Requirements for Credit Facility



			Interest and
Year Ending December 31,	Principal		Final Payment		Total
2019	$	—	$	2,474	$	2,474
2020		—		2,481		2,481
2021		8,333		2,094		10,427
2022		8,333		1,270		9,603
2023		8,334		1,319		9,653
	$	25,000	$	9,638	$	34,638

Stock-Based Awards (Tables)

12 Months Ended

Dec. 31, 2018

Stock-Based Awards

Schedule of Assumptions Used to Determine Fair Value of Stock Options Granted to Employees and Directors Presented on Weighted Average Basis


	Year Ended
	December 31,
	2018		2017		2016
Risk-free interest rate	2.65	%	2.00	%	1.42	%
Expected term (in years)	6		6		6
Expected volatility	102	%	102	%	85	%
Expected dividend yield	—	%	—	%	—	%

Schedule of Stock Option Activity


				Weighted
		Weighted		Average
		Average		Remaining	Aggregate
	Shares Issuable	Exercise		Contractual	Intrinsic
	Under Options	Price		Term	Value
				(In years)
Outstanding as of December 31, 2017	4,002,374	$	10.08	7.2	$	1,222
Granted	1,883,157		5.59
Exercised	(182,261)		2.18
Forfeited	(472,439)		10.83
Outstanding as of December 31, 2018	5,230,831	$	8.67	7.5	$	654
Options vested and expected to vest as of December 31, 2018	4,954,183	$	8.82	7.4	$	654
Options exercisable as of December 31, 2018	2,629,571	$	10.57	6.2	$	654

Schedule of Stock-Based Compensation Expense Related to Stock Options and Restricted Common Stock


	Year Ended December 31,

	2018		2017		2016
Research and development	$	2,557	$	2,584	$	1,900
Selling and marketing		449		633		490
General and administrative		4,477		4,104		3,566
	$	7,483	$	7,321	$	5,956

Net Loss Per Share (Tables)

12 Months Ended

Dec. 31, 2018

Net Loss Per Share

Schedule of Basic and Diluted Net Loss Per Share Attributable to Common Stockholders


	Year Ended December 31,
	2018		2017		2016
Numerator:
Net loss attributable to common stockholders	$	(59,978)	$	(63,386)	$	(44,703)
Denominator:
Weighted average common shares outstanding, basic and diluted		38,115,142		28,818,196		24,816,348
Net loss per share attributable to common stockholders, basic and diluted	$	(1.57)	$	(2.20)	$	(1.80)

Schedule of Antidilutive Securities, Excluded from Computation of Diluted Net Loss per Share


	December 31,
	2018	2017	2016
Options to purchase common stock	5,230,831	4,002,374	3,091,480
Warrants for the purchase of common stock	18,939	18,939	18,939
	5,249,770	4,021,313	3,110,419

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2018

Commitments and Contingencies.

Summary of Future Minimum Lease Payments for Operating Leases


Year Ending December 31,
2019		1,809
2020		1,850
2021		1,886
2022		1,936
2023		1,730
Thereafter		5,224
Total	$	14,435

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2018

Income Taxes

Reconciliation of Federal Income Tax Rate


	Year Ended December 31,
	2018		2017		2016
Federal statutory income tax rate	(21.0)	%	(34.0)	%	(34.0)	%
Tax reform change	—		43.0		—
Research and development tax credits	(3.6)		(3.3)		(2.9)
State taxes, net of federal benefit	(4.5)		(3.8)		(4.8)
Stock-based compensation	1.3		2.2		1.4
Other	0.1		(0.2)		(0.6)
Change in deferred tax asset valuation allowance	27.7		(3.9)		40.9
Effective income tax rate	—	%	—	%	—	%

Net Deferred Tax Assets


	December 31,
	2018		2017
Net operating loss carryforwards	$	49,699	$	33,094
Tax credit carryforwards		10,160		7,971
Capitalized start-up costs		870		1,022
Capitalized research and development expenses, net		18,418		21,869
Accrued expenses and other temporary differences		5,196		3,770
Total gross deferred tax assets		84,343		67,726
Valuation allowance		(84,343)		(67,726)
Net deferred tax assets	$	—	$	—

Changes in Valuation Allowance for Deferred Tax Assets


	Year Ended December 31,
	2018		2017		2016
Valuation allowance as of beginning of year	$	67,726	$	70,236	$	51,969
Increases recorded to income tax provision		16,617		24,773		18,267
Decreases recorded to income tax provision		—		(27,283)		—
Valuation allowance as of end of year	$	84,343	$	67,726	$	70,236

Restructuring and Other Costs (Tables)

12 Months Ended

Dec. 31, 2018

Restructuring and Other Costs

Summary of restructuring and other costs by category

wwe

	Twelve Months Ended December 31, 2017
	Total
Research and development	$	690
Selling and marketing		1,399
General and administration		417
	$	2,506

Summary of restructuring and other costs reserve


	Year Ended
	December 31, 2018
Restructuring and other costs at December 31, 2017	$	960
Amounts paid during the period		(960)
Restructuring and other costs at December 31, 2018	$	—

Selected Quarterly Financial Data (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2018

Selected Quarterly Financial Data (Unaudited)

Schedule of Quarterly Financial Data


	Three Months Ended
	Dec. 31,		Sept. 30,		June 30,		Mar 31,		Dec. 31,		Sept. 30,		June 30,		Mar 31,
	2018		2018		2018		2018		2017		2017		2017		2017
Statements of Operations Data:
Product revenue	$	504	$	498	$	648	$	340	$	487	$	523	$	438	$	475
Revenue		504		498		648		340		487		523		438		475
Loss from operations		(17,283)		(14,816)		(13,564)		(13,455)		(12,716)		(15,196)		(18,339)		(15,672)
Net loss		(17,399)		(15,010)		(13,804)		(13,765)		(13,102)		(15,567)		(18,694)		(16,023)
Basic and diluted net loss per common share	$	(0.42)	$	(0.38)	$	(0.37)	$	(0.40)	$	(0.44)	$	(0.54)	$	(0.64)	$	(0.58)

Nature of the Business and Basis of Presentation - Nature of Business (Details) - USD ($) $ in Thousands	1 Months Ended	2 Months Ended	3 Months Ended	12 Months Ended			26 Months Ended
	Mar. 31, 2019	Feb. 22, 2019	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2018
Nature of Business
Net proceeds from issuance of common stock				$ 61,571	$ 29,238	$ 627
Accumulated deficit				297,243	237,265		$ 297,243
Subsequent Event \| Unsecured senior subordinated convertible notes
Nature of Business
Net proceeds from issuance of convertible notes payable	$ 37,100
Common Stock \| 2016 Sales Agreement
Nature of Business
Net proceeds from issuance of common stock			$ 626	$ 26,824	$ 5,977		$ 33,427
Common Stock \| Subsequent Event \| 2016 Sales Agreement
Nature of Business
Net proceeds from issuance of common stock		$ 4,967

Summary of Significant Accounting Policies - Revenue Recognition (Details)	12 Months Ended
	Dec. 31, 2018
Summary of Significant Accounting Policies
Financing component	true
Incremental costs of obtaining contract	true
Receivables period from product shipment (in days)	30 days

Summary of Significant Accounting Policies - Inventory Valuation (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Inventory
Raw materials	$ 112	$ 68
Work-in-process	33	37
Finished goods	72	17
Total inventory	$ 217	$ 122

Summary of Significant Accounting Policies - Restricted Cash (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Restricted Cash
Restricted cash	$ 6,614	$ 6,614	$ 1,614	$ 1,728
2018 Amended Credit Facility
Restricted Cash
Minimum cash in hand as a financial covenant	5,000	5,000
Security deposit
Restricted Cash
Restricted cash	$ 6,614	$ 6,614	$ 1,614

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Summary Of Significant Accounting Policies
Income tax examination, likelihood of settlement, description	The amount of the benefit that may be recognized is the largest amount that has a greater than 50% likelihood of being realized upon ultimate settlement.
Deferred offering costs	$ 0	$ 108
Minimum
Summary Of Significant Accounting Policies
Property and equipment, estimated useful life	3 years
Income tax examination, likelihood of settlement, percentage	50.00%
Maximum
Summary Of Significant Accounting Policies
Property and equipment, estimated useful life	5 years

Summary of Significant Accounting Policies - ASU 2016-18 (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of the cash, cash equivalents, and restricted cash reported within the balance sheet that sum to the total of the same amounts shown in the statement of cash flows:
Cash and cash equivalents	$ 54,062	$ 41,538	$ 32,936
Restricted cash	6,614	1,614	1,728
Total cash, cash equivalents and restricted cash as shown on the statement of cash flow	$ 60,676	$ 43,152	$ 34,664	$ 31,012

Summary of Significant Accounting Policies - ASU 2016-02 (Details) - Scenario Forecast Adjustment - Accounting Standards Update 2016-02 $ in Thousands	Jan. 01, 2019 USD ($)
Recently Issued Accounting Pronouncements
Lease liability	$ 9,000
Right-of-use asset	$ 6,000

Fair Value of Financial Assets and Liabilities - Schedule of Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - Recurring Basis - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Assets:
Total assets at fair value	$ 50,906	$ 40,386
Money Market Funds
Assets:
Cash equivalents	50,906	40,386
Level 2
Assets:
Total assets at fair value	50,906	40,386
Level 2 \| Money Market Funds
Assets:
Cash equivalents	$ 50,906	$ 40,386

Fair Value of Financial Assets and Liabilities - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Fair Value of Financial Assets and Liabilities
Transfers between fair value measurement levels	$ 0	$ 0	$ 0

Property and Equipment, net - Schedule of Property and Equipment, net (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Property and Equipment, net
Property and equipment, gross	$ 17,863	$ 15,819
Less: Accumulated depreciation	(7,627)	(5,341)
Property and equipment, net	10,236	10,478
Equipment
Property and Equipment, net
Property and equipment, gross	7,917	6,183
Leasehold Improvements
Property and Equipment, net
Property and equipment, gross	8,675	8,553
Furniture and Fixtures
Property and Equipment, net
Property and equipment, gross	760	740
Software
Property and Equipment, net
Property and equipment, gross	180	118
Construction in Progress
Property and Equipment, net
Property and equipment, gross	$ 331	$ 225

Property and Equipment, net - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Depreciation expense	$ 2,286	$ 1,625	$ 881
Construction in Progress
Write off of manufacturing equipment			$ 1,263

Accrued Expenses and Deferred Rent - Summary (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Accrued Expenses and Deferred Rent
Accrued payroll and related expenses	$ 3,558	$ 2,936
Accrued rent	267	267
Accrued professional fees	1,393	534
Accrued research and development expenses	380	217
Accrued other	596	356
Total	$ 6,194	$ 4,310

Collaboration and Feasibility Agreements - Additional Information (Details) - Collaboration Agreement - Regeneron $ in Thousands	Oct. 10, 2016 USD ($)
Collaboration and Feasibility Agreements
Payment receivable upon exercise of option	$ 10,000
Potential payment receivable per Licensed Product upon first commercial sale of such Licensed Product	100,000
Maximum
Collaboration and Feasibility Agreements
Reimbursable clinical development costs	25,000
Potential increase in reimbursable clinical development costs	5,000
Potential payment receivable per Licensed Product upon the achievement of specified development and regulatory milestones	145,000
Potential payment receivable due for achievement of specified sales milestones for all Licensed Products	$ 50,000

Notes Payable - Additional Information (Details) $ in Thousands	1 Months Ended		12 Months Ended
	Dec. 31, 2018 USD ($) installment	Mar. 31, 2017 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Notes Payable
Outstanding borrowings under credit facility, net of unamortized discount	$ 25,000		$ 25,000	$ 18,000
2014 Credit Facility
Notes Payable
Borrowing capacity under the agreement	25,000		25,000
2017 Amended Credit Facility
Notes Payable
Outstanding borrowings under credit facility, net of unamortized discount		$ 18,000
Final payment due (as a percent)		3.50%
2017 Amended Credit Facility \| LIBOR
Notes Payable
Interest rate floor (as a percent)		1.00%
Basis spread (as a percent)		7.25%
Indicative interest rate (as a percent)		8.25%
2018 Amended Credit Facility
Notes Payable
Outstanding borrowings under credit facility, net of unamortized discount	25,000		25,000
Repayments of debt, Principal	$ 694		$ 25,000
Number of equal monthly installments \| installment	36
Final payment due (as a percent)	3.50%		3.50%
Additional final payment	$ 875		$ 875
Minimum cash in hand as a financial covenant	5,000		$ 5,000
2018 Amended Credit Facility \| Achievement of certain milestones
Notes Payable
Repayments of debt, Principal	$ 1,042
Number of equal monthly installments \| installment	24
2018 Amended Credit Facility \| LIBOR
Notes Payable
Effective annual interest rate (as a percent)	9.76%		9.76%
Interest rate floor (as a percent)	2.00%		2.00%
Basis spread (as a percent)	7.25%
2017 and 2018 Amended Credit Facility
Notes Payable
Effective annual interest rate (as a percent)	13.90%		13.90%

Notes Payable - Borrowings Outstanding (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Notes Payable.
Borrowings outstanding	$ 25,000	$ 18,000
Accrued exit fee	5	221
Unamortized discount	(217)	(205)
Borrowings	$ 24,788	$ 18,016

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References + Details

Notes Payable - Schedule of Annual Repayment Requirements for Credit Facility (Details) - 2018 Amended Credit Facility - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2018
Annual repayment requirements
Credit Facility, Principal	$ 694	$ 25,000
Credit Facility, Interest and Final Payment		9,638
Credit Facility, Total		34,638
2019
Annual repayment requirements
Credit Facility, Interest and Final Payment		2,474
Credit Facility, Total		2,474
2020
Annual repayment requirements
Credit Facility, Interest and Final Payment		2,481
Credit Facility, Total		2,481
2021
Annual repayment requirements
Credit Facility, Principal		8,333
Credit Facility, Interest and Final Payment		2,094
Credit Facility, Total		10,427
2022
Annual repayment requirements
Credit Facility, Principal		8,333
Credit Facility, Interest and Final Payment		1,270
Credit Facility, Total		9,603
2023
Annual repayment requirements
Credit Facility, Principal		8,334
Credit Facility, Interest and Final Payment		1,319
Credit Facility, Total		$ 9,653

Warrants - Additional Information (Details) - Warrants for Common Stock	Dec. 31, 2018 $ / shares shares
Warrants
Number of shares callable by warrants \| shares	18,939
Weighted Average
Warrants
Weighted average exercise price to purchase common stock \| $ / shares	$ 7.92

Preferred Stock (Details) - $ / shares	Dec. 31, 2018	Dec. 31, 2017
Preferred Stock
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0

Common Stock (Details) $ / shares in Units, $ in Thousands	1 Months Ended			3 Months Ended	12 Months Ended			26 Months Ended
Common Stock (Details) $ / shares in Units, $ in Thousands	Jan. 31, 2018 USD ($) $ / shares shares	Jan. 31, 2017 USD ($) $ / shares shares	Nov. 30, 2016 USD ($)	Dec. 31, 2016 USD ($) shares	Dec. 31, 2018 USD ($) Vote shares	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2018 USD ($) shares	Jan. 01, 2015 shares	Dec. 31, 2014 shares
Common Stock
Common stock, shares authorized					100,000,000	100,000,000		100,000,000
Number of votes per share \| Vote					1
Voting right description					Each share of common stock entitles the holder to one vote on all matters submitted to a vote of the Company's stockholders.
Net proceeds from issuance of common stock \| $					$ 61,571	$ 29,238	$ 627
Common Stock
Common Stock
Number of shares issued					11,596,173	4,359,920	102,077
Common Stock \| 2016 Sales Agreement
Common Stock
Maximum aggregate proceeds from offering \| $			$ 40,000
Number of shares issued				102,077	4,121,173	788,491		5,011,741
Net proceeds from issuance of common stock \| $				$ 626	$ 26,824	$ 5,977		$ 33,427
Common Stock \| Follow-on Offering
Common Stock
Common stock, price per share \| $ / shares	$ 5.00	$ 7.00
Number of shares issued	7,475,000	3,571,429
Net proceeds from issuance of common stock \| $	$ 34,704	$ 23,261
2014 Stock Incentive Plan \| Common Stock
Common Stock
Common stock shares, reserved					7,232,523			7,232,523	2,126,907	1,336,907

Stock-Based Awards - Additional Information (Details) - $ / shares				12 Months Ended
	Jan. 01, 2018	Jun. 20, 2017	Jan. 01, 2015	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2014
Stock-Based Awards
Options granted to purchase shares of common stock				1,883,157
Exercise price (in dollars per share)				$ 5.59
Unvested service-based stock options held by nonemployees				7,917
Common Stock
Stock-Based Awards
Issuance of common stock in connection with employee stock purchase plan, shares				81,455	53,662	66,628
2014 Stock Incentive Plan \| Common Stock
Stock-Based Awards
Number of shares of common stock authorized for issuance			2,126,907	7,232,523			1,336,907
Increased number of shares of common stock reserved for issuance			1,659,218
Additional number of shares of common stock , percentage			4.00%
Additional number of shares authorized for issuance	1,186,328
Number of shares of common stock available for issuance				1,581,243
2014 Employee Stock Purchase Plan \| Common Stock
Stock-Based Awards
Number of shares of common stock authorized for issuance			232,402				207,402
Increased number of shares of common stock reserved for issuance	148,291		207,402
Additional number of shares of common stock , percentage			0.50%
Number of shares of common stock available for issuance				401,510
Management \| Non-statutory Stock Option
Stock-Based Awards
Options granted to purchase shares of common stock		590,000
Stock options vesting period		4 years
Exercise price (in dollars per share)		$ 10.94
Percentage of shares underlying the option award vesting on first anniversary		25.00%
Percentage of shares underlying the option award vesting monthly after the first anniversary		75.00%

Stock-Based Awards - Fair Value Assumptions (Details)	12 Months Ended
Stock-Based Awards - Fair Value Assumptions (Details)	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Assumptions Used to Determine Fair Value of Stock Options Granted to Employees and Directors Presented on a Weighted Average Basis
Risk-free interest rate	2.65%	2.00%	1.42%
Expected term (in years)	6 years	6 years	6 years
Expected volatility	102.00%	102.00%	85.00%

Stock-Based Awards - Schedule of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Shares Issuable Under Options
Shares Issuable Under Options, Beginning balance	4,002,374
Shares Issuable Under Options, Granted	1,883,157
Shares Issuable Under Options, Exercised	(182,261)
Shares Issuable Under Options, Forfeited	(472,439)
Shares Issuable Under Options, Ending balance	5,230,831	4,002,374
Shares Issuable Under Options, Vested and expected to vest	4,954,183
Shares Issuable Under Options, Exercisable	2,629,571
Weighted Average Exercise Price
Weighted Average Exercise Price, Beginning balance	$ 10.08
Weighted Average Exercise Price, Granted	5.59
Weighted Average Exercise Price, Exercised	2.18
Weighted Average Exercise Price, Forfeited	10.83
Weighted Average Exercise Price, Ending balance	8.67	$ 10.08
Weighted Average Exercise Price, Vested and expected to vest	8.82
Weighted Average Exercise Price, Exercisable	$ 10.57
Weighted Average Remaining Contractual Term	7 years 6 months	7 years 2 months 12 days
Weighted Average Remaining Contractual Term, Vested and Expected to vest	7 years 4 months 24 days
Weighted Average Remaining Contractual Term, Exercisable	6 years 2 months 12 days
Other disclosures
Aggregate Intrinsic Value	$ 654	$ 1,222
Aggregate Intrinsic Value, Vested and Expected to vest	654
Aggregate Intrinsic Value, Exercisable	654
Aggregate intrinsic value of stock options exercised	$ 551	$ 408	$ 575
Weighted average fair value of stock option granted	$ 4.48	$ 6.44	$ 4.52

Stock-Based Awards - Restricted Common Stock (Details) - Restricted Common Stock. - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Restricted Common Stock
Aggregate intrinsic value of restricted stock award vested	$ 0	$ 0	$ 0
Remaining number of shares available	0	0

Stock-Based Awards - Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Stock-based Compensation
Stock-based compensation expense	$ 7,483	$ 7,321	$ 5,956
Unrecognized stock-based compensation cost	$ 11,486
Weighted average period of unrecognized stock-based compensation cost expected to be recognized	2 years 6 months
Research and Development Expense
Stock-based Compensation
Stock-based compensation expense	$ 2,557	2,584	1,900
Selling and Marketing Expense
Stock-based Compensation
Stock-based compensation expense	449	633	490
General and Administrative Expense
Stock-based Compensation
Stock-based compensation expense	$ 4,477	$ 4,104	$ 3,566

Net Loss Per Share - Basic and Diluted Net Loss Per Share Attributable to Common Stockholders (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Basic and diluted net loss per share attributable to common stockholders:
Net loss attributable to common stockholders	$ (17,399)	$ (15,010)	$ (13,804)	$ (13,765)	$ (13,102)	$ (15,567)	$ (18,694)	$ (16,023)	$ (59,978)	$ (63,386)	$ (44,703)
Weighted average common shares outstanding, basic and diluted									38,115,142	28,818,196	24,816,348
Net loss per share attributable to common stockholders, basic and diluted	$ (0.42)	$ (0.38)	$ (0.37)	$ (0.40)	$ (0.44)	$ (0.54)	$ (0.64)	$ (0.58)	$ (1.57)	$ (2.20)	$ (1.80)

Net Loss Per Share - Schedule of Antidilutive Securities, Excluded from Computation of Diluted Net Loss per Share (Details) - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share
Total common stock equivalents	5,249,770	4,021,313	3,110,419
Options to Purchase Common Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share
Total common stock equivalents	5,230,831	4,002,374	3,091,480
Warrant \| Common Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share
Total common stock equivalents	18,939	18,939	18,939

Commitments and Contingencies - Summary of Future Minimum Lease Payments for Operating Leases (Details) $ in Thousands	1 Months Ended			12 Months Ended
	Jul. 31, 2018 USD ($)	Oct. 31, 2017 USD ($)	Jun. 30, 2016 USD ($) ft²	Jul. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Jun. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Leases
Rental expense					$ 1,788		$ 1,733	$ 1,084
Future minimum lease payments
2019					1,809
2020					1,850
2021					1,886
2022					1,936
2023					1,730
Thereafter					5,224
Total					14,435
Original Lease
Leases
Security Deposit		$ 228
Second Amendment to Lease
Leases
Security Deposit		114
Base rent	$ 0					$ 524
Lease termination fee to be paid upon termination of lease agreement		$ 273
Second Amendment to Lease \| Forecast
Leases
Base rent				$ 544
Lease Agreement, June 2016, Bedford, Massachusetts
Leases
Area covered under lease \| ft²			70,712
Initial annual base rent of leased space			$ 1,200
Letter of credit			1,500
Construction costs billed to landlord							2,725
Payments received from the landlord relating to construction costs							$ 2,656
Forfeiture of construction allowance					$ 100
Lease Agreement, June 2016, Bedford, Massachusetts \| Maximum
Leases
Construction allowance under lease agreement			$ 2,800

Commitments and Contingencies - Additional Information (Details) - USD ($) $ in Thousands		3 Months Ended	144 Months Ended
	Oct. 10, 2016	Dec. 31, 2018	Dec. 31, 2018
Incept
Commitments and Contingencies
Payments for Royalties			$ 214
Regeneron \| Collaboration Agreement
Commitments and Contingencies
Payments made under the collaboration agreement		$ 0
Regeneron \| Collaboration Agreement \| Maximum
Commitments and Contingencies
Reimbursable clinical development costs	$ 25,000
Potential increase in reimbursable clinical development costs	$ 5,000

Income Taxes - U.S. Tax Reform (Details)	12 Months Ended
Income Taxes - U.S. Tax Reform (Details)	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Corporate tax rate	21.00%	34.00%	34.00%
Deduction of net operating losses to current year table income (as a percent)	80.00%
Maximum
Corporate tax rate		35.00%

Income Taxes - Reconciliation of Federal Income Tax Rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Taxes
Income tax benefit	$ 0	$ 0	$ 0
Reconciliation of the U.S. federal statutory income tax rate to the Company’s effective income tax rate
Federal statutory income tax rate	(21.00%)	(34.00%)	(34.00%)
Tax reform change		43.00%
Research and development tax credits	(3.60%)	(3.30%)	(2.90%)
State taxes, net of federal benefit	(4.50%)	(3.80%)	(4.80%)
Stock-based compensation	1.30%	2.20%	1.40%
Other	0.10%	(0.20%)	(0.60%)
Change in deferred tax asset valuation allowance	27.70%	(3.90%)	40.90%

Income Taxes - Net Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes
Net operating loss carryforwards	$ 49,699	$ 33,094
Tax credit carryforwards	10,160	7,971
Capitalized start-up costs	870	1,022
Capitalized research and development expenses, net	18,418	21,869
Accrued expenses and other temporary differences	5,196	3,770
Total gross deferred tax assets	84,343	67,726
Valuation allowance	$ (84,343)	$ (67,726)	$ (70,236)	$ (51,969)

Income Taxes - Changes in Valuation Allowance for Deferred Tax Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Taxes
Valuation allowance as of beginning of year	$ 67,726	$ 70,236	$ 51,969
Increases recorded to income tax provision	16,617	24,773	18,267
Decreases recorded to income tax provision		(27,283)
Valuation allowance as of end of year	$ 84,343	$ 67,726	$ 70,236

Income Taxes - Net Operating Loss Carryforwards (Details) $ in Thousands	Dec. 31, 2018 USD ($)
Federal
Net operating loss carryforwards
Net operating loss carryforwards	$ 190,555
Net operating loss carryforward that can be carried forward indefinitely	64,327
State
Net operating loss carryforwards
Net operating loss carryforwards	$ 161,837

Income Taxes - Tax Credit Carryforwards (Details) - Research and Development $ in Thousands	Dec. 31, 2018 USD ($)
Federal
Tax credit carryforwards
Tax credit carryforwards	$ 7,036
State
Tax credit carryforwards
Tax credit carryforwards	$ 3,611

Income Taxes - Other (Details) - USD ($) $ in Thousands	12 Months Ended
Income Taxes - Other (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Income Taxes
Increased ownership percentage	50.00%
Net increase (decrease) in deferred tax valuation allowance	$ 16,617	$ (2,510)
Unrecognized tax benefits	0	0
Accrued interest or penalties related to uncertain tax positions	0	0
Interest expense or penalties related to uncertain tax positions	$ 0	$ 0

401(k) Savings Plan - Additional Information (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($)
401(k) Savings Plan
Contributions to savings plan	$ 0

Related Party Transactions - Additional Information (Details) - USD ($) $ in Thousands	1 Months Ended		12 Months Ended
	Feb. 28, 2017	Mar. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Legal Fees \| WilmerHale
Related Party Transactions
Expenses incurred				$ 1,368	$ 874
Accounts payable				194
Accrued expenses				80
McCarter \| Legal Fees \| Senior Vice President
Related Party Transactions
Expenses incurred			$ 1,019	42
Accounts payable			$ 526
Axtria \| Master Service Agreement \| Board of Director
Related Party Transactions
Statement of work amount	$ 1,400	$ 104
Payments made				864	$ 150
Accounts payable				$ 0

Restructuring and Other Costs - Summary (Details) $ in Thousands		12 Months Ended
	Jul. 31, 2017 position	Dec. 31, 2017 USD ($)
Restructuring and other costs
Restructuring and other costs		$ 2,506
Research and Development Expense
Restructuring and other costs
Restructuring and other costs		690
Selling and Marketing Expense
Restructuring and other costs
Restructuring and other costs		1,399
General and Administrative Expense
Restructuring and other costs
Restructuring and other costs		417
Ankerud Transition Agreement
Restructuring and other costs
Severance expense		386
Fortune Transition Agreement
Restructuring and other costs
Severance expense		417
Elimination of portion of Company's workforce
Positions eliminated
Number of positions eliminated \| position	30
Restructuring and other costs
Restructuring and other costs		$ 1,703

Restructuring and Other Costs - Reserve (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($)
Reserve
Restructuring and other costs reserve beginning balance	$ 960
Amounts paid during the period	$ (960)

Selected Quarterly Financial Data (Unaudited) - Schedule of Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statements of Operations Data:
Revenues	$ 504	$ 498	$ 648	$ 340	$ 487	$ 523	$ 438	$ 475	$ 1,990	$ 1,923	$ 1,887
Loss from operations	(17,283)	(14,816)	(13,564)	(13,455)	(12,716)	(15,196)	(18,339)	(15,672)	(59,118)	(61,923)	(43,326)
Net loss	$ (17,399)	$ (15,010)	$ (13,804)	$ (13,765)	$ (13,102)	$ (15,567)	$ (18,694)	$ (16,023)	$ (59,978)	$ (63,386)	$ (44,703)
Net loss per share attributable to common stockholders, basic and diluted	$ (0.42)	$ (0.38)	$ (0.37)	$ (0.40)	$ (0.44)	$ (0.54)	$ (0.64)	$ (0.58)	$ (1.57)	$ (2.20)	$ (1.80)
Product
Statements of Operations Data:
Revenues	$ 504	$ 498	$ 648	$ 340	$ 487	$ 523	$ 438	$ 475	$ 1,990	$ 1,923	$ 1,845

Subsequent Events (Details) - USD ($) $ / shares in Units, $ in Thousands					2 Months Ended	3 Months Ended	12 Months Ended			26 Months Ended
	Mar. 07, 2019	Jan. 01, 2019	Jan. 01, 2018	Jan. 01, 2015	Feb. 22, 2019	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2018
Subsequent Events
Net proceeds from issuance of common stock							$ 61,571	$ 29,238	$ 627
Common stock, par value							$ 0.0001	$ 0.0001		$ 0.0001
Common Stock
Subsequent Events
Number of shares issued							11,596,173	4,359,920	102,077
Common Stock \| 2016 Sales Agreement
Subsequent Events
Number of shares issued						102,077	4,121,173	788,491		5,011,741
Net proceeds from issuance of common stock						$ 626	$ 26,824	$ 5,977		$ 33,427
Common Stock \| 2014 Stock Incentive Plan
Subsequent Events
Increased number of shares of common stock reserved for issuance				1,659,218
Additional number of shares of common stock , percentage				4.00%
Additional number of shares authorized for issuance			1,186,328
Common Stock \| 2014 Employee Stock Purchase Plan
Subsequent Events
Increased number of shares of common stock reserved for issuance			148,291	207,402
Additional number of shares of common stock , percentage				0.50%
Subsequent Event \| Unsecured senior subordinated convertible notes
Subsequent Events
Aggregate principal amount	$ 37,500
Number of business days to issue and sell notes from agreement date	5 days
Interest rate (as a percent)	6.00%
Common stock, par value	$ 0.0001
Maximum beneficial ownership percent	19.99%
Number of shares of common stock per $1,000 principal amount	153.8462
Initial conversion price	$ 6.50
Debt repurchase price percent	100.00%
Subsequent Event \| Unsecured senior subordinated convertible notes \| On or after March 1, 2022
Subsequent Events
Debt repurchase price percent	100.00%
Minimum percentage of common stock for conversion of debt	130.00%
Trading days for conversion of purchase price	20
Consecutive preceeding trading days for conversion of purchase price	30
Subsequent Event \| Common Stock \| 2016 Sales Agreement
Subsequent Events
Number of shares issued					1,318,481
Net proceeds from issuance of common stock					$ 4,967
Subsequent Event \| Common Stock \| 2014 Stock Incentive Plan
Subsequent Events
Additional number of shares authorized for issuance		1,659,218
Subsequent Event \| Common Stock \| 2014 Employee Stock Purchase Plan
Subsequent Events
Additional number of shares authorized for issuance		207,402