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Document and Entity Information - USD ($) $ in Millions	12 Months Ended
Document and Entity Information - USD ($) $ in Millions	Dec. 31, 2014	Mar. 13, 2015
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2014
Document Fiscal Year Focus	2014
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	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		21,415,990
Entity Public Float	$ 305

Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2014	Dec. 31, 2013
Current assets:
Cash and cash equivalents	$ 37,393	$ 17,505
Marketable securities	37,435	0
Accounts receivable from related party		19
Accounts receivable	329	250
Inventory	133
Prepaid expenses and other current assets	893	240
Total current assets	76,183	18,014
Property and equipment, net	1,782	904
Restricted cash	228	228
Total assets	78,193	19,146
Current liabilities:
Accounts payable	1,316	545
Accrued expenses	3,016	741
Deferred revenue	188	250
Notes payable, net of discount, current	1,354	1,806
Total current liabilities	5,874	3,342
Preferred stock warrants		254
Deferred rent, long-term	112	27
Notes payable, net of discount, long-term	13,511	651
Total liabilities	19,497	4,274
Commitments and contingencies (Note 13)
Redeemable convertible preferred stock (Series A, B, C, D and D-1), $0.001 par value; no shares and 33,979,025 shares authorized at December 31, 2014 and 2013, respectively; no shares and 32,842,187 shares issued and outstanding at December 31, 2014 and 2013, respectively		74,344
Stockholders' equity (deficit):
Preferred stock, $0.0001 par value; 5,000,000 and no shares authorized at December 31, 2014 and 2013, respectively; no shares issued or outstanding at December 31, 2014 and 2013
Common stock, $0.0001 par value; 100,000,000 and 45,000,000 shares authorized at December 31, 2014 and 2013, respectively; 21,333,507 and 2,676,648 shares issued and outstanding at December 31, 2014 and 2013, respectively	2
Additional paid-in capital	148,122	1,308
Accumulated deficit	(89,428)	(60,780)
Total stockholders' equity (deficit)	58,696	(59,472)
Total liabilities, redeemable convertible preferred stock and stockholders' equity (deficit)	$ 78,193	$ 19,146

Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2014	Dec. 31, 2013
Statement of Financial Position [Abstract]
Redeemable convertible preferred stock, par value	$ 0.001	$ 0.001
Redeemable convertible preferred stock, shares authorized	0	33,979,025
Redeemable convertible preferred stock, shares issued	0	32,842,187
Redeemable convertible preferred stock, shares outstanding	0	32,842,187
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	5,000,000	0
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	45,000,000
Common stock, shares issued	21,333,507	2,676,648
Common stock, shares outstanding	21,333,507	2,676,648

Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Revenue:
Collaboration revenue	$ 312
Product revenue	460		$ 10
Total revenue	772		10
Operating expenses:
Cost of product revenue	91		7
Research and development	18,880	$ 10,517	11,540
Selling and marketing	1,982	625	657
General and administrative	6,913	1,761	1,477
Total operating expenses	27,866	12,903	13,681
Loss from operations	(27,094)	(12,903)	(13,671)
Other income (expense):
Interest income	7	13	4
Interest expense	(1,119)	(441)	(377)
Other income (expense), net	(442)	14	(49)
Total other expense, net	(1,554)	(414)	(422)
Net loss and comprehensive loss	(28,648)	(13,317)	(14,093)
Accretion of redeemable convertible preferred stock to redemption value	(11)	(27)	(35)
Net loss attributable to common stockholders	$ (28,659)	$ (13,344)	$ (14,128)
Net loss per share attributable to common stockholders, basic and diluted	$ (2.69)	$ (5.11)	$ (5.60)
Weighted average common shares outstanding, basic and diluted	10,652,865	2,609,020	2,522,564

Statements of Changes in Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	General and Administrative Expense [Member]	Research and Development Expense [Member]	Series A, B, C, D and D-1 Redeemable Convertible Preferred Stock [Member]	Series A, B, C, D and D-1 Redeemable Convertible Preferred Stock [Member] Series D Preferred Stock [Member]	Series A, B, C, D and D-1 Redeemable Convertible Preferred Stock [Member] Series D-1 Redeemable Convertible Preferred Stock [Member]	Common Stock [Member]	Common Stock [Member] General and Administrative Expense [Member]	Common Stock [Member] Research and Development Expense [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member] General and Administrative Expense [Member]	Additional Paid-in Capital [Member] Research and Development Expense [Member]	Accumulated Deficit [Member]
Opening balances at Dec. 31, 2011	$ (32,729)			$ 42,004						$ 641			$ (33,370)
Opening balances, shares at Dec. 31, 2011				20,338,123			2,510,978
Issuance of common stock, shares							41,666
Issuance of common stock upon exercise of stock options	3									3
Issuance of common stock upon exercise of stock options, shares							5,409
Stock-based compensation expense	243									243
Accretion of redeemable convertible preferred stock to redemption value	(35)			$ 35						(35)
Issuance costs	(6)
Net loss	(14,093)												(14,093)
Ending balances at Dec. 31, 2012	(46,611)			$ 65,823						852			(47,463)
Ending balances, shares at Dec. 31, 2012				30,008,853			2,558,053
Issuance of preferred stock, net of issuance costs					$ 23,784
Issuance of preferred stock, net of issuance costs, shares					9,670,730
Issuance of restricted common stock	0			$ 0			$ 0			0			0
Issuance of restricted common stock, Shares							100,378
Issuance of common stock upon exercise of stock options	7									7
Issuance of common stock upon exercise of stock options, shares							18,217
Stock-based compensation expense	476									476
Accretion of redeemable convertible preferred stock to redemption value	(27)			27						(27)
Issuance costs	(6)
Net loss	(13,317)												(13,317)
Ending balances at Dec. 31, 2013	(59,472)			$ 74,344						1,308			(60,780)
Ending balances, shares at Dec. 31, 2013				32,842,187			2,676,648
Issuance of preferred stock, net of issuance costs						$ 8,494
Issuance of preferred stock, net of issuance costs, shares	0					2,833,334
Issuance of common stock and restricted common stock	$ 0			$ 0			$ 0			0			0
Issuance of common stock and restricted common stock, shares							148,227
Issuance of common stock	69,518						$ 1			69,517
Issuance of common stock, shares							5,750,000
Issuance of common stock upon exercise of stock options	$ 35									35
Issuance of common stock upon exercise of stock options, shares	44,094						44,094
Stock-based compensation expense	$ 2,644									2,644
Issuance of common stock in connection with employee stock purchase plan	64									64
Issuance of common stock in connection with employee stock purchase plan, shares							5,395
Issuance of common stock in payment		$ 699	$ 1,665								$ 699	$ 1,665
Issuance of common stock in payment, shares								79,545	189,393
Accretion of redeemable convertible preferred stock to redemption value	(11)			11						(11)
Issuance costs	(3,113)									(3,113)
Conversion of preferred stock to common stock	74,355			$ (74,355)			$ 1			74,354
Conversion of preferred stock to common stock, shares				(32,842,187)			12,440,205
Conversion of preferred stock warrants to common stock warrants	960									960
Net loss	(28,648)												(28,648)
Ending balances at Dec. 31, 2014	58,696						$ 2			$ 148,122			$ (89,428)
Ending balances, shares at Dec. 31, 2014							21,333,507
Issuance of preferred stock, net of issuance costs
Issuance of preferred stock, net of issuance costs, shares	0

Statements of Changes in Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Statement of Stockholders' Equity [Abstract]
Issuance costs	$ 3,113	$ 6	$ 6

Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
Statements of Cash Flows - USD ($) $ in Thousands	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash flows from operating activities:
Net loss	$ (28,648)	$ (13,317)	$ (14,093)
Adjustments to reconcile net loss to net cash used in operating activities
Stock-based compensation expense	2,644	476	243
Licensing and consultant fees paid in common stock	2,364
Non-cash interest expense	103	46	86
Depreciation and amortization expense	547	404	404
Revaluation of preferred stock warrants	380	(14)	49
Loss on extinguishment of debt	57
Loss on disposal of property and equipment	4
Purchase of premium on marketable securities	(133)
Amortization of premium on marketable securities	24
Changes in operating assets and liabilities:
Accounts receivable from related party	19	26	77
Accounts receivable	(79)	(250)
Prepaid expenses and other current assets	(36)	118	(114)
Inventory	(133)
Other assets			8
Accounts payable	507	(174)	145
Accrued expenses and deferred rent	1,946	(210)	610
Deferred revenue	(62)	250
Net cash used in operating activities	(20,496)	(12,645)	(12,585)
Cash flows from investing activities:
Purchases of property and equipment	(1,260)	(387)	(203)
Purchases of investments	(37,326)
Proceeds from sales or maturities of investments			4,017
Net cash provided by (used in) investing activities	(38,586)	(387)	3,814
Cash flows from financing activities:
Proceeds from issuance of redeemable convertible preferred stock, net of issuance costs		8,494	23,784
Proceeds from issuance of notes payable and preferred stock warrants	14,877		4,417
Proceeds from issuance of common stock	69,518
Proceeds from issuance of common stock pursuant to employee stock purchase plan	64
Proceeds from exercise of stock options	35	7	3
Payments of initial public offering costs	(3,018)
Payments of insurance costs financed by a third-party	(233)
Repayment of notes payable	(2,273)	(1,818)	(909)
Net cash provided by financing activities	78,970	6,683	27,295
Net increase (decrease) in cash and cash equivalents	19,888	(6,349)	18,524
Cash and cash equivalents at beginning of period	17,505	23,854	5,330
Cash and cash equivalents at end of period	37,393	17,505	23,854
Supplemental disclosure of cash flow information:
Cash paid for interest	844	289	216
Supplemental disclosure of non-cash investing and financing activities:
Accretion of redeemable convertible preferred stock to redemption value	11	27	$ 35
Conversion of redeemable convertible preferred stock to common stock	74,354
Conversion of warrants for redeemable convertible preferred stock to warrants for common stock	960
Additions to property and equipment included in accounts payable at balance sheet dates	169	$ 136
Insurance premium financed by a third party	623
Initial public offering costs included in accounts payable	$ 95

Nature of the Business and Basis of Presentation	12 Months Ended
Nature of the Business and Basis of Presentation	Dec. 31, 2014
Accounting Policies [Abstract]
Nature of the Business and Basis of Presentation	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 development and commercialization of innovative therapies for diseases and conditions of the eye using its proven, proprietary hydrogel platform technology. The Company’s bioresorbable hydrogel based product candidates are designed to provide sustained delivery of therapeutic agents to the eye. Since inception, the Company’s operations have been limited to 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, beginning in the first quarter of 2014, commercializing ReSure Sealant. In the first quarter of 2014, the Company began recognizing revenue from product sales of ReSure Sealant, which was approved in January 2014 by the U.S. Food and Drug Administration (“FDA”) as a product to close clear corneal incisions following cataract surgery. The Company was previously classified as a “development stage entity” in the Accounting Standards Codification and, as such, was required to present inception-to-date information in the Company’s statements of operations and comprehensive loss, redeemable convertible preferred stock and stockholders’ deficit, and cash flows. In June 2014, the Financial Accounting Standards Board (“FASB”) issued an accounting standards update that eliminates the concept of a development stage entity from U.S. generally accepted accounting principles and removes the related incremental reporting requirements. See Note 2 below for additional information on this new standard. The Company elected to early adopt the new standard. Accordingly, in contrast to the Company’s financial statements and the notes thereto for the year ended December 31, 2013 included in Company’s Registration Statement on Form S-1 on file with the Securities and Exchange Commission (“SEC”), the financial statements contained in this report do not include inception-to-date information. 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, 2014, the Company’s lead product candidates were in the development stage. 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 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 does not expect to generate meaningful 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. If the Company is unable to raise capital when needed or on attractive terms, the Company could be forced to delay, reduce or eliminate our 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. Although management continues to pursue these plans, there is no assurance that the Company will be successful in obtaining sufficient funding on terms acceptable to the Company to fund continuing operations, if at all. The Company believes that its existing cash and cash equivalents and marketable securities will enable it to fund its operating expenses, debt service obligations and capital expenditure requirements at least through the first half of 2016. The accompanying financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”). On July 30, 2014 the Company completed an initial public offering (“IPO”) of its common stock, which resulted in the issuance and sale of 5,000,000 shares of its common stock at a public offering price of $13.00 per share, resulting in net proceeds of approximately $57,337 after deducting underwriting discounts and other offering costs. Prior to the Company’s IPO, the Company had issued Series A, Series B, Series C, Series D and Series D-1 redeemable convertible preferred stock (collectively, the “Redeemable Preferred Stock”). Upon the closing of the IPO, all outstanding shares of the Company’s Redeemable Preferred Stock were automatically converted into 12,440,205 shares of the Company’s common stock and all outstanding warrants for the Company’s Redeemable Preferred Stock was automatically converted into warrants for the Company’s common stock. In August 2014, the underwriters of the Company’s IPO exercised their over-allotment option to purchase an additional 750,000 shares of common stock at the initial public offering price of $13.00 per share, less underwriting discounts, resulting in additional net proceeds of approximately $9,068 after deducting underwriting discounts.

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2014

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Use of Estimates

The preparation of 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 financial statements, and the reported amounts of revenues and expenses during the reporting periods. Significant estimates and assumptions reflected in these financial statements include, but are not limited to, revenue recognition, the accrual of research and development expenses and the valuation of common stock and stock-based awards and preferred stock warrants. 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

The Company recognizes revenue when the following four criteria are met in accordance with Accounting Standards Codification (“ASC”) 605, Revenue Recognition: persuasive evidence of a sales arrangement exists; delivery of goods has occurred through transfer of title and risk and rewards of ownership; the selling price is fixed or determinable; and collectability is reasonably assured.

The Company records revenue from product sales net of applicable provisions for returns, chargebacks, discounts, wholesaler management fees, government and commercial rebates, and other applicable allowances in the same period in which the related sales are recorded, based on the underlying contract terms.

The Company analyzes multiple-element arrangements based on the guidance in ASC Topic 605-25, Revenue Recognition—Multiple-Element Arrangements (“ASC 605-25”). Pursuant to this guidance, the Company evaluates multiple-element arrangements to determine (1) the deliverables included in the arrangement and (2) whether the individual deliverables represent separate units of accounting or whether they must be accounted for as a combined unit of accounting. This evaluation involves subjective determinations and requires management to make judgments about the individual deliverables and whether such deliverables are separable from the other aspects of the contractual relationship. Deliverables are considered separate units of accounting provided that: the delivered item has value to the customer on a standalone basis and, if the arrangement includes a general right of return relative to the delivered item, delivery or performance of the undelivered item is considered probable and substantially in the control of the Company. In assessing whether an item has standalone value, the Company considers factors such as the research, manufacturing and commercialization capabilities of the collaboration partner and the availability of the associated expertise in the general marketplace. In addition, the Company considers whether the collaboration partner can use the other deliverables for their intended purpose without the receipt of the remaining elements, whether the value of the deliverable is dependent on the undelivered items and whether there are other vendors that can provide the undelivered elements.

Arrangement consideration that is fixed or determinable is allocated among the separate units of accounting using the relative selling price method. Then, the applicable revenue recognition criteria in ASC 605 are applied to each of the separate units of accounting in determining the appropriate period and pattern of recognition. The Company determines the selling price of a unit of accounting following the hierarchy of evidence prescribed by ASC 605-25. Accordingly, the Company determines the estimated selling price for units of accounting within each arrangement using vendor-specific objective evidence (“VSOE”) of selling price, if available; third-party evidence (“TPE”) of selling price, if VSOE is not available; or best estimate of selling price (“BESP”), if neither VSOE nor TPE is available. The Company typically uses BESP to estimate the selling price as it generally does not have VSOE or TPE of selling price for its units of accounting. Determining the BESP for a unit of accounting requires significant judgment. In developing the BESP for a unit of accounting, the Company considers applicable market conditions and relevant entity-specific factors, including factors that were contemplated in negotiating the agreement with the customer and estimated costs. The Company validates the BESP for units of accounting by evaluating whether changes in the key assumptions used to determine the BESP will have a significant effect on the allocation of arrangement consideration between multiple units of accounting.

The Company recognizes arrangement consideration allocated to each unit of accounting when all of the revenue recognition criteria in ASC 605 are satisfied for that particular unit of accounting. The Company will recognize as revenue arrangement consideration attributed to licenses that have standalone value relative to the other deliverables to be provided in an arrangement upon delivery. The Company will recognize as revenue arrangement consideration attributed to licenses that do not have standalone value relative to the other deliverables to be provided in an arrangement over the Company’s estimated performance period, as the arrangement would be accounted for as a single unit of accounting.

At the inception of an arrangement that includes milestone payments, the Company evaluates whether each milestone is substantive and at risk to both parties on the basis of the contingent nature of the milestone. This evaluation includes an assessment of whether: (i) the consideration is commensurate with either the Company’s performance to achieve the milestone or the enhancement of the value of the delivered item(s) as a result of a specific outcome resulting from the Company’s performance to achieve the milestone, (ii) the consideration relates solely to past performance, and (iii) the consideration is reasonable relative to all of the deliverables and payment terms within the arrangement. The Company evaluates factors such as the scientific, clinical, regulatory, commercial and other risks that must be overcome to achieve the respective milestone and the level of effort and investment required to achieve the respective milestone in making this assessment. There is considerable judgment involved in determining whether a milestone satisfies all of the criteria required to conclude that a milestone is substantive. Accordingly, pursuant to the guidance of ASC Topic 605-28, Revenue Recognition—Milestone Method (“ASC 605-28”), revenue from milestone payments will be recognized in its entirety upon successful accomplishment of the milestone, assuming all other revenue recognition criteria are met.

Other contingent, event-based payments received for which payment is either contingent solely upon the passage of time or the results of a collaborative partner’s performance would not be considered milestones under ASC 605-28. In accordance with ASC 605-25, such payments will be recognized as revenue when all of the four basic revenue recognition criteria are met.

Whenever the Company determines that an element is delivered over a period of time, revenue is recognized using either a proportional performance model or a straight-line model over the period of performance. At each reporting period, the Company reassesses its cumulative measure of performance and makes appropriate adjustments, if necessary. The Company recognizes revenue using the proportional performance model whenever the Company can make reasonably reliable estimates of the level of effort required to complete its performance obligations under an arrangement. Revenue recognized under the proportional performance model at each reporting period is determined by multiplying the total expected payments under the contract (excluding payments contingent upon achievement of milestones) by the ratio of the level of effort incurred to date to the estimated total level of effort required to complete the performance obligations under the arrangement. Revenue is limited to the lesser of the cumulative amount of payments received or the cumulative amount of revenue earned, as determined using the proportional performance model as of each reporting period. Alternatively, if the Company cannot make reasonably reliable estimates the level of effort required to complete its performance obligations under an arrangement, then revenue under the arrangement is recognized on a straight-line basis over the period expected to complete the Company’s performance obligations. If and when a contingent milestone payment is earned, the additional consideration to be received is added to the total expected payments under the contract. Revenue is limited to the lesser of the cumulative amount of payments received or the cumulative amount of revenue earned, as determined on a straight-line basis as of the period end date. If the Company cannot reasonably estimate when its performance obligation period ends, then revenue is deferred until the Company can reasonably estimate when the performance obligation period ends.

Inventory Valuation

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

Prior to approval by the 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. Inventory costs totaling $51 were expensed during the year ended December 31, 2013 prior to obtaining FDA approval of ReSure Sealant. The Company also reviews its inventories for potential obsolescence.

The Company had inventory of $133 as of December 31, 2014, which consisted primarily of raw materials.

Restricted Cash

As of December 31, 2014 and 2013, the Company held a certificate of deposit to collateralize a credit card account with its bank of $60. This amount is included in prepaid expenses and other current assets on the Company’s balance sheet. As of December 31, 2014 and 2013, the Company also held a certificate of deposit of $228, which is a security deposit for the lease of the Company’s corporate headquarters. The Company has classified this as long-term restricted cash on its balance sheet.

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 and marketable securities. The Company has all cash and cash equivalents and marketable securities 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, marketable securities and its preferred stock warrant liabilities are carried at fair value determined according to the fair value hierarchy described above (see 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. The carrying value of the Company’s outstanding notes payable (see Note 7) approximates fair value (a level 2 fair value measurement), as estimated by the Company using a discounted cash flow analysis, reflecting discount rates currently available to the Company.

Marketable Securities

The Company’s marketable securities are classified as available-for-sale and are carried at fair value with the unrealized gains and losses reported as a component of accumulated other comprehensive income (loss) in stockholders’ equity. Realized gains and losses and declines in value judged to be other than temporary are included as a component of other income (expense), net based on the specific identification method. Fair value is determined based on quoted market prices. At December 31, 2014, marketable securities by security type consisted of:


	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
United States treasury notes	$	10,026	$	—	$	—	$	10,026
Agency bonds		27,409		—		—		27,409

Total	$	37,435	$	—	$	—	$	37,435

At December 31, 2014, marketable securities consisted of investments that mature within one year. The Company did not have marketable securities as of December 31, 2013.

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. To date, the Company has not recorded any impairment losses on 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, 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. These agreements are generally cancelable, 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 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 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. Potential for recovery of deferred tax assets is evaluated by estimating the future taxable profits expected and considering prudent and feasible tax planning strategies.

The Company accounts for uncertainty in income taxes recognized in the 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 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 hydrogel therapeutic products 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 (deficit) that result from transactions and economic events other than those with stockholders. For the years ended December 31, 2014, 2013 and 2012, there was no difference between net loss and comprehensive loss.

Net Income (Loss) Per Share

Prior to the closing of its IPO of common stock, the Company followed the two-class method when computing net income (loss) per share, as the Company had outstanding shares that met the definition of participating securities. The two-class method 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 and warrants for the purchase of Redeemable Preferred Stock. 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.

The Company’s Redeemable Preferred Stock outstanding prior to the IPO, contractually entitled the holders of such shares to participate in dividends but did not contractually require the holders of such shares to participate in losses of the Company. Similarly, 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, 2014, 2013 and 2012.

Recently Issued and Adopted Accounting Pronouncements

In August 2014, the FASB issued Accounting Standards Update (“ASU”) 2014-15, Presentation of Financial Statements—Going Concern (Subtopic 205-40). The new guidance addresses management’s responsibility to evaluate whether there is substantial doubt about an entity’s ability to continue as a going concern and to provide related footnote disclosures. Management’s evaluation should be based on relevant conditions and events that are known and reasonably knowable at the date that the financial statements are issued. The standard will be effective for the first interim period within annual reporting periods beginning after December 15, 2016. Early adoption is permitted. The Company is evaluating the effect that this guidance will have on its financial statements and footnote disclosures.

In June 2014, the FASB issued ASU 2014-10, Development Stage Entities (Topic 915): Elimination of Certain Financial Reporting Requirements, Including an Amendment to Variable Interest Entities Guidance in Topic 810, Consolidation. The amendments in this guidance remove all incremental financial reporting requirements for development stage entities. Among other changes, this guidance will no longer require development stage entities to present inception-to-date information about income statement line items, cash flows, and equity transactions. This guidance is effective for public companies in the first annual period beginning after December 15, 2014. The Company elected to apply this disclosure guidance to its financial statements for the year ended December 31, 2014 and as a result, no longer discloses inception-to-date information in its statements of operations and comprehensive loss, cash flows and stockholders’ deficit and the related notes thereto.

In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606), (“ASU 2014-09”). ASU 2014-09 outlines a new, single comprehensive model for entities to use in accounting for revenue arising from contracts with customers and supersedes most current revenue recognition guidance, including industry-specific guidance. This new revenue recognition model provides a five-step analysis in determining when and how revenue is recognized. The new model will require revenue recognition to depict the transfer of promised goods or services to customers in an amount that reflects the consideration a company expects to receive in exchange for those goods or services. ASU 2014-09 is effective for public entities for annual reporting periods beginning after December 15, 2016 and interim periods within those periods. Early adoption is not permitted. Companies may use either a full retrospective or a modified retrospective approach to adopt ASU 2014-09. The Company is currently assessing the impact that adopting this new accounting guidance will have on its financial statements and footnote disclosures.

Fair Value of Financial Assets and Liabilities

12 Months Ended

Dec. 31, 2014

Fair Value Disclosures [Abstract]

Fair Value of Financial Assets and Liabilities

3. Fair Value of Financial Assets and Liabilities

The following tables present information about the Company’s assets and liabilities that are measured at fair value on a recurring basis as of December 31, 2014 and 2013 and indicate the level of the fair value hierarchy utilized to determine such fair value:


	Fair Value Measurements as of December 31, 2014 Using:
	Level 1		Level 2		Level 3		Total
Assets:
Cash equivalents:
Money market funds	$	—	$	29,103	$	—	$	29,103
Agency bonds		—		7,599		—		7,599
Marketable securities:
United States treasury notes		—		10,026		—		10,026
Agency bonds		—		27,409		—		27,409

Total	$	—	$	74,137	$	—	$	74,137


	Fair Value Measurements as of December 31, 2013 Using:
	Level 1		Level 2		Level 3		Total
Assets:
Cash equivalents:
Money market funds	$	—	$	17,272	$	—	$	17,272

Liabilities:
Liability for preferred stock warrants	$	—	$	—	$	254	$	254

During the years ended December 31, 2014, 2013 and 2012, there were no transfers between Level 1, Level 2 and Level 3.

The warrant liability in the table above is comprised of the values of warrants for the purchase of Series A, B and D redeemable convertible preferred stock and was based on significant inputs not observable in the market, which represented a Level 3 measurement within the fair value hierarchy. The Company’s valuation of the redeemable convertible preferred stock warrants utilized the Black-Scholes option-pricing model, which incorporates assumptions and estimates to value the preferred stock warrants. The Company assessed these assumptions and estimates on a quarterly basis as additional information impacting the assumptions was obtained. Changes in the fair value of the redeemable convertible preferred stock warrants were recognized in the statements of operations.

Related to the valuation of the warrants, the quantitative elements associated with the Company’s Level 3 inputs impacting fair value measurement included the fair value per share of the underlying Series A, Series B and Series D redeemable convertible preferred stock, the remaining contractual term of the warrants, risk-free interest rate, expected dividend yield, and expected volatility of the price of the underlying preferred stock. The Company determined the fair value per share of the underlying preferred stock by taking into consideration its most recent sales of its redeemable convertible preferred stock as well as additional factors that the Company deemed relevant. The Company historically has been a private company and lacked company-specific historical and implied volatility information of its stock. Therefore, it estimated its expected stock volatility based on the historical volatility of publicly traded peer companies for a term equal to the remaining contractual term of the warrants. The risk-free interest rate was determined by reference to the U.S. Treasury yield curve for time periods approximately equal to the remaining contractual term of the warrants. The Company estimated a 0% dividend yield based on the expected dividend yield and the fact that the Company has never paid or declared dividends.

The following table provides a rollforward of the aggregate fair values of the Company’s preferred stock warrants for which fair value was determined by level 3 inputs:


Balance, January 1, 2012	$	219
Increase in fair value		49

Balance, December 31, 2012		268
Decrease in fair value		(14	)

Balance, December 31, 2013		254
Issuance of Series D-1 warrants		326
Increase in fair value		380
Conversion of preferred stock warrants to common stock warrants (see Note 8)		(960	)

Balance, December 31, 2014	$	—

- 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, 2014

Property, Plant and Equipment [Abstract]

Property and Equipment, net

4. Property and Equipment, net

Property and equipment, net consisted of the following as of December 31, 2014 and 2013:


	December 31,
	2014			2013
Equipment	$	2,606		$	1,806
Leasehold improvements		815			398
Furniture and fixtures		295			145
Software		25			25
Construction in progress		262			205

		4,003			2,579
Less: Accumulated depreciation		(2,221	)		(1,675	)

	$	1,782		$	904

Depreciation expense was $547, $404 and $404 for the years ended December 31, 2014, 2013 and 2012, respectively.

The construction in progress is related to the build-out of a clean room, which commenced in 2013.

Accrued Expenses

12 Months Ended

Dec. 31, 2014

Payables and Accruals [Abstract]

Accrued Expenses

5. Accrued Expenses

Accrued expenses consisted of the following as of December 31, 2014 and 2013:


	December 31,
	2014		2013
Accrued payroll and related expenses	$	1,495	$	464
Accrued professional fees		338		90
Accrued research and development expenses		540		82
Accrued insurance		389		—
Accrued other		254		105

	$	3,016	$	741

Feasibility Agreement	12 Months Ended
Feasibility Agreement	Dec. 31, 2014
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Feasibility Agreement	6. Feasibility Agreement In September 2013, the Company entered into a feasibility agreement with a biopharmaceutical company. Under this agreement, the biopharmaceutical company will pay up to $500 for completing certain tasks and achieving certain milestones. In the event that the agreement is terminated in advance of the completion of the tasks/achievement of the milestones, the Company would be required to refund portions of the amounts received, based on the actual work completed/milestones achieved as of the date of termination. As of December 31, 2013, no milestones had been achieved and, accordingly, the Company did not record any revenue related to this agreement. As of December 31, 2013, the Company had accounts receivable and deferred revenue of $250 related to this agreement recorded on its balance sheet. In the fourth quarter of 2014, the Company completed the tasks related to the first milestone at which time the $250 became non-refundable and therefore the Company recorded revenue of $250. The biopharmaceutical company has indicated that they will not proceed with the second phase of the agreement. The Company does not have any further obligations in connection with this agreement. In October 2014, the Company entered into a feasibility agreement with a biotechnology company. Under this agreement, the biotechnology company will pay up to $700, of which $250 was a non-refundable payment due upon contract execution and $450 will be due upon the achievement of certain milestones. The Company is recognizing the non-contingent revenue of $250 on a straight-line basis over the twelve-month period expected to complete the Company’s performance obligations. If and when a contingent milestone payment is earned, the additional consideration to be received will be added to the total expected payments under the contract. As of December 31, 2014, the Company has recognized revenue of $63, has deferred revenue of $187 and has $250 in accounts receivable related to this agreement. In January 2015, we achieved the first milestone under the feasibility agreement triggering a payment due of $250.

Notes Payable

12 Months Ended

Dec. 31, 2014

Debt Disclosure [Abstract]

Notes Payable

7. Notes Payable

The Company entered into a credit agreement with a lending institution in 2011 (the “2011 Modification Agreement”) which had a total borrowing capacity of $5,000 which was fully drawn down. Borrowings under the agreement were required to be repaid in 33 monthly installments commencing July 1, 2012 of $152, plus interest on the principal balance at a rate of the greater of (i) 4.75% above the lender’s prime rate or (ii) 8% per annum. In addition to these principal payments, the Company was required to make a final payment of $225 in March 2015 (or upon earlier termination of the agreement) to the lender, which amount was being accreted to the carrying value of the debt, using the effective interest method. The effective annual interest rate of the outstanding debt under the 2011 Modification Agreement was approximately 11%.

On April 17, 2014, the Company entered into a credit and security agreement (the “2014 Credit Facility”) and terminated the 2011 Modification Agreement. The 2014 Credit Facility provides for initial borrowings of $15,000 under a term loan (“Tranche 1 loan”) and additional borrowings of up to $5,000 under a term loan (“Tranche 2 loan”), for a maximum of $20,000. On that same date, the Company received proceeds of $15,000 through the issuance of promissory notes to the lenders under the Tranche 1 loan. Upon the completion of the IPO in July 2014, borrowings under the Tranche 2 loan became available through December 31, 2014. The Company did not draw down the $5,000 available under the Tranche 2 loan prior to its expiration, and this amount is no longer available to the Company. All promissory notes issued under the 2014 Credit Facility mature on April 1, 2018 and are collateralized by substantially all of the Company’s personal property, other than its intellectual property. There are no financial covenants associated with the 2014 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 obligations under the 2014 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 Company is obligated to make monthly, interest-only payments on the Tranche 1 loan funded under the 2014 Credit Facility until September 30, 2015 and, thereafter, to pay 30 consecutive, equal monthly installments of principal from October 1, 2015 through March 1, 2018 plus interest. The Tranche 1 loan under the 2014 Credit Facility bears interest at an annual rate of 8.25%. In addition, a final payment equal to 3.75% of any amounts drawn under the 2014 Credit Facility is due upon its maturity date.

In connection with the Tranche 1 loan, the lenders received warrants to purchase 100,000 shares of the Company’s Series D-1 redeemable convertible preferred stock with an exercise price of $3.00 per share, which are exercisable until April 2021. The fair value of the warrants as of the issuance date totaling $326 was recorded as a preferred stock warrant liability (see Note 8). Of this amount, $290 was allocated to the 2014 Credit Facility and recorded as debt discount and $36 was allocated to the 2011 Modification Agreement and recorded as loss on extinguishment of debt (see below). As of December 31, 2014, the effective annual interest rate of the outstanding debt under the 2014 Credit Facility was approximately 11%.

The terms of the 2014 Credit Facility required that the existing outstanding borrowings be repaid. Accordingly, on April 17, 2014, the Company used $1,898 of proceeds from the Tranche 1 loan to repay all amounts then due under the 2011 Modification Agreement, consisting of $1,667 of principal, $6 of interest and $225 of a final payment.

The Company accounted for the termination of the 2011 Modification Agreement as an extinguishment in accordance with the guidance in ASC 470-50, Debt. The total amount of unamortized debt discount of $10 is reflected as a loss on extinguishment of debt and included in other expense within the statements of operations and comprehensive loss. Additionally, fees paid to the lenders that were allocated to the existing debt and treated as an extinguishment, inclusive of the value of warrants issued and debt issuance costs paid, totaling $47, were also reflected as a loss on extinguishment of debt included in other expense within the statements of operations and comprehensive loss.

As of December 31, 2014, the annual repayment requirements for the 2014 Credit Facility, inclusive of the final payment of $563 due at expiration, were as follows:


Year Ending December 31,	Principal		Interest and Final Payment		Total
2015	$	1,500	$	1,244	$	2,744
2016		6,000		902		6,902
2017		6,000		397		6,397
2018		1,500		583		2,083

	$	15,000	$	3,126	$	18,126

Warrants	12 Months Ended
Warrants	Dec. 31, 2014
Text Block [Abstract]
Warrants	8. Warrants The Company previously had outstanding warrants for the purchase of 236,836 shares of preferred stock. Effective upon the closing of the Company’s IPO in July 2014, the Company’s outstanding preferred stock warrants became warrants for the purchase of 89,708 shares of common stock at a weighted average exercise price of $6.32 per share. Through December 31, 2014, no warrants have been exercised and warrants for the purchase of 89,708 shares of common stock remain outstanding at December 31, 2014.

Redeemable Convertible Preferred Stock

12 Months Ended

Dec. 31, 2014

Equity [Abstract]

Redeemable Convertible Preferred Stock

9. Redeemable Convertible Preferred Stock

Prior to the Company’s IPO, the Company had issued Series A, Series B, Series C, Series D and Series D-1 redeemable convertible preferred stock (collectively, the “Redeemable Preferred Stock”). The Redeemable Preferred Stock was classified outside of stockholders’ equity (deficit) because the shares contained redemption features that were not solely within the control of the Company.

During 2012, the Company issued 9,670,730 shares of Series D redeemable convertible preferred stock at an issuance price equal to $2.46 per share and received gross proceeds of $23,790. In connection with this financing, the Company paid total issuance costs of $6.

During 2013, the Company issued 2,833,334 shares of Series D-1 redeemable convertible preferred stock at an issuance price equal to $3.00 per share and received gross proceeds of $8,500. In connection with this financing, the Company paid total issuance costs of $6.

On July 10, 2014, the Company effected a 1-for-2.64 reverse stock split of its issued and outstanding shares of common stock and a proportional adjustment to the existing conversion ratios for each series of Redeemable Preferred Stock. Accordingly, all share and per share amounts for all periods presented in these financial statements and notes thereto have been adjusted retroactively, where applicable, to reflect this reverse stock split and adjustment of the preferred stock conversion ratios.

Redeemable Preferred Stock consisted of the following as of December 31, 2013:


	Preferred Shares Authorized		Preferred Shares Issued and Outstanding		Liquidation Preference		Carrying Value		Common Stock Issuable Upon Conversion
Series A redeemable convertible preferred stock		1,172,836		1,145,836	$	1,146	$	1,145		434,028
Series B redeemable convertible preferred stock		3,306,189		3,257,329		6,000		5,989		1,233,835
Series C redeemable convertible preferred stock		10,500,000		10,243,901		21,000		20,973		3,880,260
Series D redeemable convertible preferred stock		16,000,000		15,361,787		37,790		37,742		5,818,850
Series D-1 redeemable convertible preferred stock		3,000,000		2,833,334		8,500		8,495		1,073,232

		33,979,025		32,842,187	$	74,436	$	74,344		12,440,205

Upon the closing of the Company’s IPO in July 2014, all outstanding shares of the Company’s Redeemable Preferred Stock were converted into 12,440,205 shares of common stock.

Prior to the conversion, the rights and preferences of the Company’s outstanding Redeemable Preferred Stock were as follows:

Voting Rights

The holders of Redeemable Preferred Stock were entitled to vote, together with the holders of common stock, on all matters submitted to stockholders for a vote. Each holder of Redeemable Preferred Stock was entitled to cast the number of votes equal to the number of whole shares of common stock into which such Redeemable Preferred Stock could convert on the record date for determination of stockholders entitled to vote.

Dividends

The holders of the Redeemable Preferred Stock, in order of preference, were entitled to receive, out of funds that were legally available, noncumulative dividends when and if declared by the board of directors. No dividends had been declared by the Company prior to the conversion.

Liquidation Preference

In the event of any voluntary or involuntary liquidation, dissolution or winding up of the Company (each, a “Liquidation Event”), the redeemable convertible preferred stockholders were entitled to be paid out of the assets of the Company in the order and preference as specified in the Company’s previous certificate of incorporation, as amended and restated.

Conversion

Each share of Redeemable Preferred Stock was convertible into common stock at the option of the stockholder at any time after the date of issuance and were automatically converted into shares of common stock upon the closing of the Company’s IPO in July 2014 on a 2.64-for-1 basis.

Redemption Rights

At the written election of at least 60% of the holders of the Redeemable Preferred Stock, voting together as a single class on an as-converted basis, the shares of such Redeemable Preferred Stock outstanding were redeemable, at any time on or after May 31, 2018, in three equal annual installments commencing sixty days after receipt of the required vote, in an amount equal to the Original Issue Price per share of Redeemable Preferred Stock plus all declared but unpaid dividends thereon.

The carrying values of the Redeemable Preferred Stock was being accreted to their redemption values through their respective redemption dates.

- Definition

The entire disclosure for shareholders' equity comprised of portions attributable to the parent entity and noncontrolling interest, including other comprehensive income. Includes, but is not limited to, balances of common stock, preferred stock, additional paid-in capital, other capital and retained earnings, accumulated balance for each classification of other comprehensive income and amount of comprehensive income.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(d),(e))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21484-112644

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SAB TOPIC 4.E)
-URI http://asc.fasb.org/extlink&oid=27010918&loc=d3e74512-122707

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21488-112644

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.29-31)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 4
-Subparagraph (SAB TOPIC 4.C)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187143-122770

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21506-112644

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 30
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6405834&loc=d3e23285-112656

Reference 10: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21475-112644

Reference 11: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Preferred Stock
-URI http://asc.fasb.org/extlink&oid=6521494

Reference 12: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644

Reference 13: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21564-112644

Reference 14: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 08
-Paragraph d
-Article 4

Reference 15: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 29, 30, 31
-Article 5

Reference 16: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Staff Accounting Bulletin (SAB)
-Number Topic 4
-Section E

Reference 17: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 08
-Article 4

Reference 18: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Staff Accounting Bulletin (SAB)
-Number Topic 4
-Section C

Reference 19: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 04
-Article 3

+ Details

Common Stock and Preferred Stock	12 Months Ended
Common Stock and Preferred Stock	Dec. 31, 2014
Text Block [Abstract]
Common Stock and Preferred Stock	10. Common Stock and Preferred Stock On July 30, 2014 the Company completed its IPO, which resulted in the sale of 5,000,000 shares of its common stock at a public offering price of $13.00 per share. Upon closing of the IPO, all outstanding shares of the Company’s redeemable convertible preferred stock were automatically converted into 12,440,205 shares of common stock. Additionally upon closing the IPO, the Company adopted an amended and restated certificate of incorporation increasing the number of its authorized shares of its common stock to 100,000,000 shares. In conjunction with the IPO and the amended and restated certificate of incorporation, the Company is authorized to issue 5,000,000 shares of preferred stock, $0.0001 par value, all of which is undesignated. On August 19, 2014, the Company completed the sale of an additional 750,000 shares of common stock at the initial public offering price of $13.00 per share to the underwriters of the Company’s IPO pursuant to the exercise of their over-allotment option. The Company received additional net proceeds of approximately $9,068 after deducting underwriting discounts and offering costs. Each share of common stock entitles the holder to one vote on all matters submitted to a vote of the Company’s stockholders. As of December 31, 2014 the Company had reserved 3,196,228 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 Option Plan and the number of shares available for issuance under the 2014 Employee Stock Purchase Plan (see Note 11), and the outstanding warrants to purchase common stock (see Note 8).

Stock-Based Awards

12 Months Ended

Dec. 31, 2014

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Stock-Based Awards

11. Stock-Based Awards

2006 Stock Option Plan

The Company’s 2006 Stock Option Plan, as amended (the “2006 Plan”), provides for the Company to sell or issue common stock or restricted common stock, or to grant incentive stock options or nonqualified stock options for the purchase of common stock, to employees, members of the board of directors and consultants of the Company. The 2006 Plan is administered by the board of directors, or at the discretion of the board of directors, by a committee of the board. The exercise prices, vesting and other restrictions are determined at the discretion of the board of directors, or their committee if so delegated, except that the exercise price per share of stock options may not be less than 100% of the fair market value of the share of common stock on the date of grant and the term of stock options may not be greater than ten years.

Stock options granted under the 2006 Plan generally vest over four years and expire after ten years, although options have been granted with vesting terms less than four years.

On July 30, 2014, the Company’s 2014 Stock Incentive Plan (the “2014 Plan”) became effective and no further stock options or other awards will be made under the 2006 Plan. Shares of common stock that were available for grant under the 2006 Plan as of July 30, 2014 as well as any shares of common stock subject to awards under the 2006 Plan that expire, terminate, or are otherwise surrendered, cancelled, forfeited or repurchased without having been fully exercised or resulting in any common stock being issued will become available for issuance under the 2014 Plan, up to a specified number of shares.

2014 Stock Incentive Plan

On June 19, 2014, the Company’s stockholders approved the 2014 Plan, which became effective immediately prior to the closing of the Company’s IPO on July 30, 2014. 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 originally reserved for issuance under the 2014 Plan, inclusive of shares from the 2006 Plan, was 1,336,907. As of December 31, 2014, 1,292,522 shares remain available for issuance under the 2014 Plan. 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 December 23, 2014, the board of directors adopted a resolution to increase the number available under the 2014 Plan by an additional 790,000 shares effective as of January 1, 2015.

The Company generally grants stock-based awards with service conditions only (“service-based” awards).

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.

2014 Employee Stock Purchase Plan

On June 19, 2014, the Company’s stockholders approved the 2014 Employee Stock Purchase Plan (the “ESPP”). A total of 207,402 shares of common stock are reserved for issuance under this plan. The ESPP became effective immediately prior to the closing of the Company’s IPO on July 30, 2014. In addition, 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. The Company’s first offering period commenced October 1, 2014 and closed on December 31, 2014 at which time 5,395 shares of common stock were issued for total proceeds of $64. As of December 31, 2014, 202,007 shares of common stock remain available for issuance. On December 23, 2014, the board of directors adopted a resolution to increase the number of authorized under the ESPP by an additional 25,000 shares effective as of January 1, 2015.

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. Prior to the Company’s IPO in July 2014, the Company had been a private company and lacked company-specific historical and implied volatility information. Therefore, it 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. 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, 2014, there were outstanding unvested service-based stock options held by nonemployees for the purchase of 9,587 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,
	2014			2013			2012
Risk-free interest rate		2.24	%		1.23	%		1.51	%
Expected term (in years)		5.96			5.38			6.25
Expected volatility		76.5	%		74.6	%		70.0	%
Expected dividend yield		0	%		0	%		0	%

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


	Shares Issuable Under Options			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
						(In years)
Outstanding as of December 31, 2013		924,132		$	1.69		7.0	$	1,986
Granted		753,886			9.35
Exercised		(44,094	)		0.78
Forfeited		(21,933	)		5.56

Outstanding as of December 31, 2014		1,611,991		$	5.24		6.5	$	29,464

Options vested and expected to vest as of December 31, 2014		1,603,423		$	5.26		6.5	$	29,279

Options exercisable as of December 31, 2014		651,303		$	1.72		4.8	$	14,196

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 $323, $38 and $6 during the years ended December 31, 2014, 2013 and 2012, respectively.

The weighted average grant date fair value of stock options granted to employees and directors during the years ended December 31, 2014, 2013 and 2012 was $6.55, $1.51 and $0.87 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. There was no restricted common stock activity in 2013. The table below summarizes the Company’s restricted stock activity in 2014:


	Shares			Weighted Average Grant Date Fair Value
Unvested restricted common stock as of December 31, 2013		—			—
Issued		123,134		$	8.80
Vested		(94,697	)	$	8.80
Forfeited		—			—

Unvested restricted common stock as of December 31, 2014		28,437		$	8.80

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. The aggregate intrinsic value of restricted stock awards that vested during the years ended December 31, 2014, 2013 and 2012 was $1,142, $278 and $10, respectively.

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,
	2014		2013		2012
Research and development	$	397	$	70	$	67
Selling and marketing		68		22		28
General and administrative		2,179		384		148

	$	2,644	$	476	$	243

As of December 31, 2014, the Company had an aggregate of $4,342 of unrecognized stock-based compensation cost, which is expected to be recognized over a weighted average period of 2.9 years.

Net Loss Per Share and Unaudited Pro Forma Net Loss Per Share

12 Months Ended

Dec. 31, 2014

Earnings Per Share [Abstract]

Net Loss Per Share and Unaudited Pro Forma Net Loss Per Share

12. Net Loss Per Share and Unaudited Pro Forma Net Loss Per Share

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, 2014, 2013 and 2012:


	Year Ended December 31,
	2014			2013			2012
Numerator:
Net loss	$	(28,648	)	$	(13,317	)	$	(14,093	)
Accretion of redeemable convertible preferred stock to redemption value		(11	)		(27	)		(35	)

Net loss attributable to common stockholders	$	(28,659	)	$	(13,344	)	$	(14,128	)

Denominator:
Weighted average common shares outstanding, basic and diluted		10,652,865			2,609,020			2,522,564

Net loss per share attributable to common stockholders, basic and diluted	$	(2.69	)	$	(5.11	)	$	(5.60	)

The Company excluded the following common stock equivalents, outstanding as of December 31, 2014, 2013 and 2012, from the computation of diluted net loss per share attributable to common stockholders for the years ended December 31, 2014, 2013 and 2012 because they had an anti-dilutive impact due to the net loss attributable to common stockholders incurred for the periods.


	December 31,
	2014		2013		2012
Options to purchase common stock		1,611,991		924,132		615,377
Non-vested restricted common stock		28,437		—		6,992
Warrants for the purchase of redeemable convertible preferred stock		—		51,830		51,830
Warrants for the purchase of common stock		89,708		—		—
Redeemable convertible preferred stock (as converted to common stock)		—		12,440,205		11,366,973

		1,730,136		13,416,167		12,041,172

Commitments and Contingencies

12 Months Ended

Dec. 31, 2014

Commitments and Contingencies Disclosure [Abstract]

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 June 2017 and June 2018.

On April 25, 2014, the Company entered into an amendment to its lease of office, laboratory and manufacturing space in Bedford, Massachusetts. The lease amendment provides for additional office space effective as of July 2014, with a term expiring in June 2017, and also extends the term of the original lease until June 2018.

Future minimum lease payments for its operating leases as of December 31, 2014 are as follows:


Years Ending December 31,
2015	$	802
2016		820
2017		676
2018		262

Total	$	2,560

During the years ended December 31, 2014, 2013 and 2012, the Company recognized $649, $448 and $436, 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”) (see 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, 2014, royalties payable under this agreement related to product sales were not material.

On February 12, 2014, the Company issued to Incept 189,393 shares of its common stock in connection with the expansion of the scope of the license to include back of the eye technology held by Incept (see Note 16).

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 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 financial statements as of December 31, 2014.

Income Taxes

12 Months Ended

Dec. 31, 2014

Income Tax Disclosure [Abstract]

Income Taxes

14. Income Taxes

During the years ended December 31, 2014, 2013 and 2012, the Company recorded no income tax benefits for the net operating losses incurred in each year or interim period, 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,
	2014			2013			2012
Federal statutory income tax rate		(34.0	)%		(34.0	)%		(34.0	)%
Federal and state research and development tax credit		(2.5	)		(6.6	)		(1.2	)
State taxes, net of federal benefit		(4.6	)		(4.8	)		(5.1	)
Stock-based compensation		1.6			1.3			0.3
Other		0.8			—			—
Change in deferred tax asset valuation allowance		38.7			44.1			40.0

Effective income tax rate		0.0	%		0.0	%		0.0	%

Net deferred tax assets as of December 31, 2014 and 2013 consisted of the following:


	December 31,
	2014			2013
Net operating loss carryforwards	$	15,243		$	9,204
Research and development tax credit carryforwards		2,582			2,005
Capitalized start-up costs		2,204			2,426
Capitalized research and development expenses, net		15,746			11,571
Accrued expenses and other temporary differences		1,050			570

Total gross deferred tax assets		36,825			25,776
Valuation allowance		(36,825	)		(25,776	)

Net deferred tax assets	$	—		$	—

Changes in the valuation allowance for deferred tax assets during the years ended December 31, 2014, 2013 and 2012 related primarily to the increase in net operating loss carryforwards, capitalized research and development expenses and research and development tax credit carryforwards and were as follows:


	Year Ended December 31,
	2014		2013		2012
Valuation allowance as of beginning of year	$	25,776	$	19,815	$	14,171
Decreases recorded as benefit to income tax provision		—		—		—
Increases recorded to income tax provision		11,049		5,961		5,644

Valuation allowance as of end of year	$	36,825	$	25,776	$	19,815

As of December 31, 2014 the Company had net operating loss carryforwards for federal and state income tax purposes of $39,231 and $36,923, respectively, which begin to expire in 2026 and 2030, respectively. Included in the federal and state net operating loss carryforwards are approximately $114 of deductions related to the exercise of stock options which tax benefit will be realized when it results in the reduction of cash income tax in accordance with ASC 718. As of December 31, 2014, the Company also had available research and development tax credit carryforwards for federal and state income tax purposes of $1,784 and $1,208, respectively, which begin to expire in 2026 and 2024, 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, including the Company’s history of cumulative net losses incurred since inception and has concluded that it is more likely than not that the Company will not realize the benefits of the deferred tax assets. Accordingly, a full valuation allowance has been established against the deferred tax assets as of December 31, 2014 and 2013. Management reevaluates the positive and negative evidence at each reporting period.

The Company has not recorded any amounts for unrecognized tax benefits as of December 31, 2014 or 2013.

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 2011 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.

401(k) Savings Plan	12 Months Ended
401(k) Savings Plan	Dec. 31, 2014
Postemployment Benefits [Abstract]
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, 2014, no contributions have been made to the plan by the Company.

Related Party Transactions	12 Months Ended
Related Party Transactions	Dec. 31, 2014
Related Party Transactions [Abstract]
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. On February 12, 2014, the Company issued 189,393 shares of its common stock to Incept in connection with the expansion of the scope of the Incept License to include back of the eye technology held by Incept. The fair value of the shares of $1,665 as of the issuance date was recorded as research and development expense. Incept and certain owners of Incept participated in the Company’s Series A, Series B and Series C preferred stock financing and have also been granted shares of common stock and redeemable convertible preferred stock of the Company. In addition, certain employees of the Company are shareholders of Incept. The Company’s President and Chief Executive Officer is a general partner of Incept. On February 12, 2014, the Company issued 79,545 shares of common stock to a former member of the Company’s board of directors and current stockholder of Incept for consulting services rendered. The fair value of the shares of $699 as of the issuance date was recorded as general and administrative expense. During the years ended December 31, 2014, 2013 and 2012, the Company invoiced Augmenix, Inc. (“Augmenix”) $82, $232 and $366, respectively, for consulting and other services. During the years ended December 31, 2014, 2013 and 2012, Augmenix invoiced the Company $27, $0 and $0 for legal fees paid by Augmenix on behalf of the Company. During the years ended December 31, 2014, 2013 and 2012, Augmenix invoiced the Company $0, $14 and $0 respectively, for consulting services. Certain shareholders of Augmenix were holders of the Company’s redeemable convertible preferred stock and common stock which is now entirely common stock. In addition, certain employees of the Company are shareholders of Augmenix. Through December 31, 2014, the Company’s President and Chief Executive was Chairman of the board of directors of Augmenix.

- Definition

The entire disclosure for related party transactions. Examples of related party transactions include transactions between (a) a parent company and its subsidiary; (b) subsidiaries of a common parent; (c) and entity and its principal owners; and (d) affiliates.

+ References + Details

Selected Quarterly Financial Data (Unaudited)

12 Months Ended

Dec. 31, 2014

Quarterly Financial Information Disclosure [Abstract]

Selected Quarterly Financial Data (Unaudited)

17. Selected Quarterly Financial Data (Unaudited)


	Three Months Ended
	Dec. 31, 2014			Sept. 30, 2014			June 30, 2014			Mar 31, 2014			Dec. 31, 2013			Sept. 30, 2013			June 30, 2013			Mar 31, 2013
Statements of Operations Data:
Revenue	$	505		$	143		$	97		$	27		$	—		$	—		$	—		$	—
Loss from operations		(7,547	)		(6,776	)		(5,946	)		(6,825	)		(3,419	)		(3,435	)		(2,989	)		(3,060	)
Net loss		(7,954	)		(7,294	)		(6,392	)		(7,008	)		(3,505	)		(3,522	)		(3,090	)		(3,200	)
Net loss attributable to common stockholders		(7,954	)		(7,294	)		(6,397	)		(7,014	)		(3,510	)		(3,527	)		(3,099	)		(3,208	)
Basic and diluted net loss attributable to common stockholders per share	$	(0.37	)	$	(0.48	)	$	(2.10	)	$	(2.45	)	$	(1.32	)	$	(1.34	)	$	(1.19	)	$	(1.26	)

The fourth quarter of 2014 includes collaboration revenue of $312.

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2014

Accounting Policies [Abstract]

Use of Estimates

Use of Estimates

Cash Equivalents

Cash Equivalents

Revenue Recognition

Revenue Recognition

Inventory Valuation

Inventory Valuation

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

The Company had inventory of $133 as of December 31, 2014, which consisted primarily of raw materials.

Restricted Cash

Restricted Cash

Concentration of Credit Risk and of Significant Suppliers

Concentration of Credit Risk and of Significant Suppliers

Fair Value Measurements

Fair Value Measurements

•

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

•

Marketable Securities

Marketable Securities


	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
United States treasury notes	$	10,026	$	—	$	—	$	10,026
Agency bonds		27,409		—		—		27,409

Total	$	37,435	$	—	$	—	$	37,435

At December 31, 2014, marketable securities consisted of investments that mature within one year. The Company did not have marketable securities as of December 31, 2013.

Property and Equipment

Property and Equipment

Impairment of Long-Lived Assets

Impairment of Long-Lived Assets

Research and Development Costs

Research and Development Costs

Research Contract Costs and Accruals

Research Contract Costs and Accruals

Patent Costs

Patent Costs

Accounting for Stock-Based Compensation

Accounting for Stock-Based Compensation

Income Taxes

Income Taxes

Segment Data

Segment Data

Comprehensive Loss

Comprehensive Loss

Net Income (Loss) Per Share

Net Income (Loss) Per Share

Recently Issued and Adopted Accounting Pronouncements

Recently Issued and Adopted Accounting Pronouncements

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2014

Accounting Policies [Abstract]

Summary of Marketable Securities by Security Type

At December 31, 2014, marketable securities by security type consisted of:


	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
United States treasury notes	$	10,026	$	—	$	—	$	10,026
Agency bonds		27,409		—		—		27,409

Total	$	37,435	$	—	$	—	$	37,435

Fair Value of Financial Assets and Liabilities (Tables)

12 Months Ended

Dec. 31, 2014

Fair Value Disclosures [Abstract]

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


	Fair Value Measurements as of December 31, 2014 Using:
	Level 1		Level 2		Level 3		Total
Assets:
Cash equivalents:
Money market funds	$	—	$	29,103	$	—	$	29,103
Agency bonds		—		7,599		—		7,599
Marketable securities:
United States treasury notes		—		10,026		—		10,026
Agency bonds		—		27,409		—		27,409

Total	$	—	$	74,137	$	—	$	74,137


	Fair Value Measurements as of December 31, 2013 Using:
	Level 1		Level 2		Level 3		Total
Assets:
Cash equivalents:
Money market funds	$	—	$	17,272	$	—	$	17,272

Liabilities:
Liability for preferred stock warrants	$	—	$	—	$	254	$	254

Schedule of Aggregate Fair Values of Preferred Stock Warrants Determined by Level 3 Inputs

The following table provides a rollforward of the aggregate fair values of the Company’s preferred stock warrants for which fair value was determined by level 3 inputs:


Balance, January 1, 2012	$	219
Increase in fair value		49

Balance, December 31, 2012		268
Decrease in fair value		(14	)

Balance, December 31, 2013		254
Issuance of Series D-1 warrants		326
Increase in fair value		380
Conversion of preferred stock warrants to common stock warrants (see Note 8)		(960	)

Balance, December 31, 2014	$	—

Property and Equipment, net (Tables)

12 Months Ended

Dec. 31, 2014

Property, Plant and Equipment [Abstract]

Schedule of Property and Equipment net

Property and equipment, net consisted of the following as of December 31, 2014 and 2013:


	December 31,
	2014			2013
Equipment	$	2,606		$	1,806
Leasehold improvements		815			398
Furniture and fixtures		295			145
Software		25			25
Construction in progress		262			205

		4,003			2,579
Less: Accumulated depreciation		(2,221	)		(1,675	)

	$	1,782		$	904

Accrued Expenses (Tables)

12 Months Ended

Dec. 31, 2014

Payables and Accruals [Abstract]

Schedule of Accrued Expenses

Accrued expenses consisted of the following as of December 31, 2014 and 2013:


	December 31,
	2014		2013
Accrued payroll and related expenses	$	1,495	$	464
Accrued professional fees		338		90
Accrued research and development expenses		540		82
Accrued insurance		389		—
Accrued other		254		105

	$	3,016	$	741

Notes Payable (Tables)

12 Months Ended

Dec. 31, 2014

Debt Disclosure [Abstract]

Schedule of Annual Repayment Requirements for Credit Facility

As of December 31, 2014, the annual repayment requirements for the 2014 Credit Facility, inclusive of the final payment of $563 due at expiration, were as follows:


Year Ending December 31,	Principal		Interest and Final Payment		Total
2015	$	1,500	$	1,244	$	2,744
2016		6,000		902		6,902
2017		6,000		397		6,397
2018		1,500		583		2,083

	$	15,000	$	3,126	$	18,126

Redeemable Convertible Preferred Stock (Tables)

12 Months Ended

Dec. 31, 2014

Equity [Abstract]

Summary of Redeemable Preferred Stock

Redeemable Preferred Stock consisted of the following as of December 31, 2013:


	Preferred Shares Authorized		Preferred Shares Issued and Outstanding		Liquidation Preference		Carrying Value		Common Stock Issuable Upon Conversion
Series A redeemable convertible preferred stock		1,172,836		1,145,836	$	1,146	$	1,145		434,028
Series B redeemable convertible preferred stock		3,306,189		3,257,329		6,000		5,989		1,233,835
Series C redeemable convertible preferred stock		10,500,000		10,243,901		21,000		20,973		3,880,260
Series D redeemable convertible preferred stock		16,000,000		15,361,787		37,790		37,742		5,818,850
Series D-1 redeemable convertible preferred stock		3,000,000		2,833,334		8,500		8,495		1,073,232

		33,979,025		32,842,187	$	74,436	$	74,344		12,440,205

- Definition

Tabular disclosure of an entity's stock, including par or stated value per share, number and dollar amount of share subscriptions, shares authorized, shares issued, shares outstanding, number and dollar amount of shares held in an employee trust, dividend per share, total dividends, share conversion features, par value plus additional paid in capital, the value of treasury stock and other information necessary to a fair presentation, and EPS information. Stock by class includes common, convertible, and preferred stocks which are not redeemable or redeemable solely at the option of the issuer. Includes preferred stock with redemption features that are solely within the control of the issuer and mandatorily redeemable stock if redemption is required to occur only upon liquidation or termination of the reporting entity. If more than one issue is outstanding, state the title of each issue and the corresponding dollar amount; dollar amount of any shares subscribed but unissued and the deduction of subscriptions receivable there from; number of shares authorized, issued, and outstanding.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21506-112644

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 480
-SubTopic 10
-Section S99
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=27011957&loc=d3e177068-122764

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21553-112644

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(d),(e))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21475-112644

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6403732&loc=d3e21300-112643

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21521-112644

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.28,29)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 10: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21484-112644

Reference 11: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21538-112644

Reference 12: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21488-112644

Reference 13: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 30
-Article 5

Reference 14: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 29
-Article 5

+ Details

Stock-Based Awards (Tables)

12 Months Ended

Dec. 31, 2014

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Schedule of Fair Value of Stock Options Weighted Average

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,
	2014			2013			2012
Risk-free interest rate		2.24	%		1.23	%		1.51	%
Expected term (in years)		5.96			5.38			6.25
Expected volatility		76.5	%		74.6	%		70.0	%
Expected dividend yield		0	%		0	%		0	%

Schedule of stock option activity

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


	Shares Issuable Under Options			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
						(In years)
Outstanding as of December 31, 2013		924,132		$	1.69		7.0	$	1,986
Granted		753,886			9.35
Exercised		(44,094	)		0.78
Forfeited		(21,933	)		5.56

Outstanding as of December 31, 2014		1,611,991		$	5.24		6.5	$	29,464

Options vested and expected to vest as of December 31, 2014		1,603,423		$	5.26		6.5	$	29,279

Options exercisable as of December 31, 2014		651,303		$	1.72		4.8	$	14,196

Schedule of Restricted Stock Activity

The table below summarizes the Company’s restricted stock activity in 2014:


	Shares			Weighted Average Grant Date Fair Value
Unvested restricted common stock as of December 31, 2013		—			—
Issued		123,134		$	8.80
Vested		(94,697	)	$	8.80
Forfeited		—			—

Unvested restricted common stock as of December 31, 2014		28,437		$	8.80

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


	Year Ended December 31,
	2014		2013		2012
Research and development	$	397	$	70	$	67
Selling and marketing		68		22		28
General and administrative		2,179		384		148

	$	2,644	$	476	$	243

Net Loss Per Share and Unaudited Pro Forma Net Loss Per Share (Tables)

12 Months Ended

Dec. 31, 2014

Earnings Per Share [Abstract]

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

Basic and diluted net loss per share attributable to common stockholders was calculated as follows for the years ended December 31, 2014, 2013 and 2012:


	Year Ended December 31,
	2014			2013			2012
Numerator:
Net loss	$	(28,648	)	$	(13,317	)	$	(14,093	)
Accretion of redeemable convertible preferred stock to redemption value		(11	)		(27	)		(35	)

Net loss attributable to common stockholders	$	(28,659	)	$	(13,344	)	$	(14,128	)

Denominator:
Weighted average common shares outstanding, basic and diluted		10,652,865			2,609,020			2,522,564

Net loss per share attributable to common stockholders, basic and diluted	$	(2.69	)	$	(5.11	)	$	(5.60	)

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


	December 31,
	2014		2013		2012
Options to purchase common stock		1,611,991		924,132		615,377
Non-vested restricted common stock		28,437		—		6,992
Warrants for the purchase of redeemable convertible preferred stock		—		51,830		51,830
Warrants for the purchase of common stock		89,708		—		—
Redeemable convertible preferred stock (as converted to common stock)		—		12,440,205		11,366,973

		1,730,136		13,416,167		12,041,172

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2014

Commitments and Contingencies Disclosure [Abstract]

Summary of Future Minimum Lease Payments for Operating Leases

Future minimum lease payments for its operating leases as of December 31, 2014 are as follows:


Years Ending December 31,
2015	$	802
2016		820
2017		676
2018		262

Total	$	2,560

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2014

Income Tax Disclosure [Abstract]

Reconciliation of Federal Income Tax Rate

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,
	2014			2013			2012
Federal statutory income tax rate		(34.0	)%		(34.0	)%		(34.0	)%
Federal and state research and development tax credit		(2.5	)		(6.6	)		(1.2	)
State taxes, net of federal benefit		(4.6	)		(4.8	)		(5.1	)
Stock-based compensation		1.6			1.3			0.3
Other		0.8			—			—
Change in deferred tax asset valuation allowance		38.7			44.1			40.0

Effective income tax rate		0.0	%		0.0	%		0.0	%

Net Deferred Tax Assets

Net deferred tax assets as of December 31, 2014 and 2013 consisted of the following:


	December 31,
	2014			2013
Net operating loss carryforwards	$	15,243		$	9,204
Research and development tax credit carryforwards		2,582			2,005
Capitalized start-up costs		2,204			2,426
Capitalized research and development expenses, net		15,746			11,571
Accrued expenses and other temporary differences		1,050			570

Total gross deferred tax assets		36,825			25,776
Valuation allowance		(36,825	)		(25,776	)

Net deferred tax assets	$	—		$	—

Changes in Valuation Allowance for Deferred Tax Assets


	Year Ended December 31,
	2014		2013		2012
Valuation allowance as of beginning of year	$	25,776	$	19,815	$	14,171
Decreases recorded as benefit to income tax provision		—		—		—
Increases recorded to income tax provision		11,049		5,961		5,644

Valuation allowance as of end of year	$	36,825	$	25,776	$	19,815

Selected Quarterly Financial Data (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2014

Quarterly Financial Information Disclosure [Abstract]

Schedule of Quarterly Financial Data


	Three Months Ended
	Dec. 31, 2014			Sept. 30, 2014			June 30, 2014			Mar 31, 2014			Dec. 31, 2013			Sept. 30, 2013			June 30, 2013			Mar 31, 2013
Statements of Operations Data:
Revenue	$	505		$	143		$	97		$	27		$	—		$	—		$	—		$	—
Loss from operations		(7,547	)		(6,776	)		(5,946	)		(6,825	)		(3,419	)		(3,435	)		(2,989	)		(3,060	)
Net loss		(7,954	)		(7,294	)		(6,392	)		(7,008	)		(3,505	)		(3,522	)		(3,090	)		(3,200	)
Net loss attributable to common stockholders		(7,954	)		(7,294	)		(6,397	)		(7,014	)		(3,510	)		(3,527	)		(3,099	)		(3,208	)
Basic and diluted net loss attributable to common stockholders per share	$	(0.37	)	$	(0.48	)	$	(2.10	)	$	(2.45	)	$	(1.32	)	$	(1.34	)	$	(1.19	)	$	(1.26	)

Nature of the Business and Basis of Presentation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands			12 Months Ended
	Aug. 19, 2014	Jul. 30, 2014	Dec. 31, 2014	Dec. 31, 2012
Class of Stock [Line Items]
Proceeds from issuance of shares			$ 69,518
Common Stock [Member]
Class of Stock [Line Items]
Initial public offering, shares issued			5,750,000	41,666
Number of common shares issued on conversion of redeemable convertible preferred stock			12,440,205
IPO [Member]
Class of Stock [Line Items]
Proceeds from issuance of shares		$ 57,337
IPO [Member] \| Common Stock [Member]
Class of Stock [Line Items]
Initial public offering, shares issued		5,000,000
Common stock, price per share		$ 13.00
Number of common shares issued on conversion of redeemable convertible preferred stock		12,440,205
Over-allotment Option [Member]
Class of Stock [Line Items]
Proceeds from issuance of shares	$ 9,068
Over-allotment Option [Member] \| Common Stock [Member]
Class of Stock [Line Items]
Initial public offering, shares issued	750,000
Common stock, price per share	$ 13.00

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Summary Of Significant Accounting Policies [Line Items]
Inventory Cost		$ 51
Inventory net	$ 133
Certificate of deposit	$ 228	228
Maturity period of marketable securities	1 year
Marketable securities	$ 37,435	0
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.
Income tax examination, likelihood of settlement, percentage	50.00%
Certificates of Deposit [Member]
Summary Of Significant Accounting Policies [Line Items]
Certificate of deposit	$ 60	60
Certificate of deposit	$ 228	$ 228
Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Property and equipment, estimated useful life	3 years
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Property and equipment, estimated useful life	5 years

Summary of Significant Accounting Policies - Summary of Marketable Securities by Security Type (Detail) $ in Thousands	Dec. 31, 2014 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 37,435
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Estimated Fair Value	37,435
United States Treasury Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	10,026
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Estimated Fair Value	10,026
Agency Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	27,409
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Estimated Fair Value	$ 27,409

Fair Value of Financial Assets and Liabilities - Schedule of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2014	Dec. 31, 2013
Assets:
Marketable securities	$ 37,435	$ 0
Recurring Basis [Member]
Assets:
Total assets at fair value	74,137
Recurring Basis [Member] \| Preferred Stock Warrants [Member]
Liabilities:
Liability for preferred stock warrants		254
Recurring Basis [Member] \| Agency Bonds [Member]
Assets:
Cash equivalents	7,599
Marketable securities	27,409
Recurring Basis [Member] \| United States Treasury Notes [Member]
Assets:
Marketable securities	10,026
Money Market Funds [Member] \| Recurring Basis [Member]
Assets:
Cash equivalents	29,103	17,272
Level 2 [Member] \| Recurring Basis [Member]
Assets:
Total assets at fair value	74,137
Level 2 [Member] \| Recurring Basis [Member] \| Agency Bonds [Member]
Assets:
Cash equivalents	7,599
Marketable securities	27,409
Level 2 [Member] \| Recurring Basis [Member] \| United States Treasury Notes [Member]
Assets:
Marketable securities	10,026
Level 2 [Member] \| Money Market Funds [Member] \| Recurring Basis [Member]
Assets:
Cash equivalents	$ 29,103	17,272
Level 3 [Member] \| Recurring Basis [Member] \| Preferred Stock Warrants [Member]
Liabilities:
Liability for preferred stock warrants		$ 254

Fair Value of Financial Assets and Liabilities - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Transfers between fair value measurement levels	$ 0	$ 0	$ 0
Estimated dividend yield	0.00%

Fair Value of Financial Assets and Liabilities - Schedule of Aggregate Fair Values of Preferred Stock Warrants Determined by Level 3 Inputs (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 254	$ 268	$ 219
Increase/Decrease in fair value	380	(14)	49
Conversion of preferred stock warrants to common stock warrants (see Note 8)	(960)
Ending Balance		$ 254	$ 268
Series D-1 Warrants [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Issuance of warrants	$ 326

Property and Equipment, net - Schedule of Property and Equipment, net (Detail) - USD ($) $ in Thousands	Dec. 31, 2014	Dec. 31, 2013
Property, Plant and Equipment [Line Items]
Property and Equipment, gross	$ 4,003	$ 2,579
Less: Accumulated depreciation	(2,221)	(1,675)
Property and equipment, net	1,782	904
Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and Equipment, gross	2,606	1,806
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and Equipment, gross	815	398
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property and Equipment, gross	295	145
Software [Member]
Property, Plant and Equipment [Line Items]
Property and Equipment, gross	25	25
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Property and Equipment, gross	$ 262	$ 205

Property and Equipment,Net - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Property Plant And Equipment Capitalized Interest Costs [Abstract]
Depreciation expense	$ 547	$ 404	$ 404

Accrued Expenses - Schedule of Accrued Expenses (Detail) - USD ($) $ in Thousands	Dec. 31, 2014	Dec. 31, 2013
Payables and Accruals [Abstract]
Accrued payroll and related expenses	$ 1,495	$ 464
Accrued professional fees	338	90
Accrued research and development expenses	540	82
Accrued insurance	389
Accrued other	254	105
Total	$ 3,016	$ 741

Feasibility Agreement - Additional Information (Detail) - USD ($)	1 Months Ended	3 Months Ended	12 Months Ended
	Oct. 31, 2014	Dec. 31, 2014	Dec. 31, 2014	Dec. 31, 2013	Jan. 31, 2015	Sep. 30, 2013
Revenue Recognition [Line Items]
Revenue recognized		$ 312,000	$ 312,000
Accounts receivable		329,000	329,000	$ 250,000
Deferred revenue		188,000	188,000	250,000
Feasibility Agreement [Member] \| Biopharmaceutical [Member]
Revenue Recognition [Line Items]
Maximum revenue that could be recognized						$ 500,000
Revenue recognized		250,000		0
Accounts receivable				250,000
Deferred revenue				$ 250,000
Non-Refundable revenue		250,000	250,000
Feasibility Agreement [Member] \| Biotechnology [Member]
Revenue Recognition [Line Items]
Maximum revenue that could be recognized	$ 450,000
Revenue recognized			63,000
Accounts receivable		250,000	250,000
Deferred revenue		$ 187,000	187,000
Revenue recognized	700,000
Non-Refundable revenue	$ 250,000
Non-contingent revenue			$ 250,000
Feasibility Agreement [Member] \| Biotechnology [Member] \| Subsequent Event [Member]
Revenue Recognition [Line Items]
Milestone payment due					$ 250,000

Notes Payable - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
	Apr. 17, 2014	Dec. 31, 2014	Jul. 31, 2014
Line of Credit Facility [Line Items]
Exercise price of warrants granted			$ 6.32
Loss on extinguishment of debt		$ (57)
2011 Modification Agreement [Member]
Line of Credit Facility [Line Items]
Borrowing capacity under the agreement		$ 5,000
Credit facility, Monthly repayment period		33 monthly installments
Outstanding borrowings, Monthly repayment amount		$ 152
Outstanding borrowings, Interest rate above prime lending rate		4.75%
Outstanding borrowings, Interest rate		8.00%
Outstanding borrowings, Effective annual interest rate		11.00%
Proceeds from (repayments of) lines of credit	$ (1,898)
Debt discount		$ 10
Loss on extinguishment of debt		36
Outstanding borrowings, Principal	1,667
Outstanding borrowings, Interest	6
Additional final payment	225
2011 Modification Agreement [Member] \| Extinguishment of Debt [Member]
Line of Credit Facility [Line Items]
Fees paid to lenders		47
2014 Credit Facility [Member]
Line of Credit Facility [Line Items]
Borrowing capacity under the agreement	20,000
Outstanding borrowings, Monthly repayment amount		$ 15,000
Outstanding borrowings, Effective annual interest rate		11.00%
Loan and Security Agreement date		Apr. 17, 2014
Credit facility, Final payment percent of amounts drawn under the facility		3.75%
Outstanding borrowings, Interest		$ 3,126
Additional final payment		$ 563
2014 Credit Facility [Member] \| Promissory Notes [Member]
Line of Credit Facility [Line Items]
Proceeds from (repayments of) lines of credit	15,000
Debt instrument, Maturity date		Apr. 01, 2018
2014 Credit Facility [Member] \| Tranche 1 Loan [Member]
Line of Credit Facility [Line Items]
Borrowing capacity under the agreement	15,000
Credit facility, Monthly repayment period		30 consecutive, equal monthly installments
Outstanding borrowings, Interest rate		8.25%
Last installment payment		Mar. 01, 2018
First date of principal repayment		Oct. 01, 2015
Warrants to purchase redeemable convertible preferred stock granted		100,000
Exercise price of warrants granted		$ 3.00
Warrants, Date from which warrants or rights exercisable		Apr. 30, 2021
Grant date fair value of warrants granted as preferred stock warrant liability		$ 326
Debt discount		$ 290
2014 Credit Facility [Member] \| Tranche 2 Loan [Member]
Line of Credit Facility [Line Items]
Borrowing capacity under the agreement	$ 5,000

Notes Payable - Schedule of Annual Repayment Requirements for Credit Facility (Detail) - 2014 Credit Facility [Member] $ in Thousands	12 Months Ended
	Dec. 31, 2014 USD ($)
Line of Credit Facility [Line Items]
Credit Facility, Principal	$ 15,000
Credit Facility, Interest and Final Payment	3,126
Credit Facility, Total	18,126
2015 [Member]
Line of Credit Facility [Line Items]
Credit Facility, Principal	1,500
Credit Facility, Interest and Final Payment	1,244
Credit Facility, Total	2,744
2016 [Member]
Line of Credit Facility [Line Items]
Credit Facility, Principal	6,000
Credit Facility, Interest and Final Payment	902
Credit Facility, Total	6,902
2017 [Member]
Line of Credit Facility [Line Items]
Credit Facility, Principal	6,000
Credit Facility, Interest and Final Payment	397
Credit Facility, Total	6,397
2018 [Member]
Line of Credit Facility [Line Items]
Credit Facility, Principal	1,500
Credit Facility, Interest and Final Payment	583
Credit Facility, Total	$ 2,083

Warrants - Additional Information (Detail) - $ / shares	Dec. 31, 2014	Jul. 31, 2014
Class of Warrant or Right [Line Items]
Weighted average exercise price to purchase common stock		$ 6.32
Warrants exercised	0
Warrants for Preferred Stock [Member]
Class of Warrant or Right [Line Items]
Number of shares called by warrants	236,836
Warrants for Common Stock [Member]
Class of Warrant or Right [Line Items]
Number of shares called by warrants		89,708

Redeemable Convertible Preferred Stock - Additional Information (Detail)			12 Months Ended
	Jul. 30, 2014 $ / shares shares	Jul. 10, 2014	Dec. 31, 2014 USD ($) shares	Dec. 31, 2013 USD ($) $ / shares shares	Dec. 31, 2012 USD ($) $ / shares shares
Class of Stock [Line Items]
Redeemable convertible preferred stock issued \| shares			0	32,842,187
Proceeds from issuance of redeemable convertible preferred stock				$ 8,494,000	$ 23,784,000
Payment of issuance costs			$ 3,018,000
Reverse stock split conversion description			the Company effected a 1-for-2.64 reverse stock split of its issued and outstanding shares of common stock and a proportional adjustment to the existing conversion ratios for each series of Redeemable Preferred Stock.
Reverse stock split ratio		0.378
Reverse stock split, effective date			Jul. 10, 2014
Dividends declared			$ 0
Redemption description			At the written election of at least 60% of the holders of the Redeemable Preferred Stock, voting together as a single class on an as-converted basis, the shares of such Redeemable Preferred Stock outstanding were redeemable, at any time on or after May 31, 2018, in three equal annual installments commencing sixty days after receipt of the required vote, in an amount equal to the Original Issue Price per share of Redeemable Preferred Stock plus all declared but unpaid dividends thereon.
Preferred stock redemption date			May 31, 2018
Common Stock [Member]
Class of Stock [Line Items]
Number of common shares issued on conversion of redeemable convertible preferred stock \| shares			12,440,205
IPO [Member]
Class of Stock [Line Items]
Reverse stock split conversion description			Each share of Redeemable Preferred Stock was convertible into common stock at the option of the stockholder at any time after the date of issuance and were automatically converted into shares of common stock upon the closing of the Company’s IPO in July 2014 on a 2.64-for-1 basis.
IPO [Member] \| Common Stock [Member]
Class of Stock [Line Items]
Redeemable convertible preferred stock issuance price per share \| $ / shares	$ 13.00
Number of common shares issued on conversion of redeemable convertible preferred stock \| shares	12,440,205
Series D Redeemable Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Redeemable convertible preferred stock issued \| shares				15,361,787	9,670,730
Redeemable convertible preferred stock issuance price per share \| $ / shares					$ 2.46
Proceeds from issuance of redeemable convertible preferred stock					$ 23,790,000
Payment of issuance costs					$ 6,000
Series D-1 Redeemable Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Redeemable convertible preferred stock issued \| shares				2,833,334
Redeemable convertible preferred stock issuance price per share \| $ / shares				$ 3.00
Proceeds from issuance of redeemable convertible preferred stock				$ 8,500,000
Payment of issuance costs				$ 6,000

Redeemable Convertible Preferred Stock - Summary of Redeemable Preferred Stock (Detail) - USD ($) $ in Thousands	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Class of Stock [Line Items]
Redeemable Preferred Shares Authorized	0	33,979,025
Redeemable Preferred Shares Outstanding	0	32,842,187
Liquidation Preference		$ 74,436
Carrying Value		$ 74,344
Common Stock Issuable Upon Conversion		12,440,205
Preferred Shares Issued	0	32,842,187
Series A Redeemable Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Redeemable Preferred Shares Authorized		1,172,836
Redeemable Preferred Shares Outstanding		1,145,836
Liquidation Preference		$ 1,146
Carrying Value		$ 1,145
Common Stock Issuable Upon Conversion		434,028
Preferred Shares Issued		1,145,836
Series B Redeemable Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Redeemable Preferred Shares Authorized		3,306,189
Redeemable Preferred Shares Outstanding		3,257,329
Liquidation Preference		$ 6,000
Carrying Value		$ 5,989
Common Stock Issuable Upon Conversion		1,233,835
Preferred Shares Issued		3,257,329
Series C Redeemable Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Redeemable Preferred Shares Authorized		10,500,000
Redeemable Preferred Shares Outstanding		10,243,901
Liquidation Preference		$ 21,000
Carrying Value		$ 20,973
Common Stock Issuable Upon Conversion		3,880,260
Preferred Shares Issued		10,243,901
Series D Redeemable Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Redeemable Preferred Shares Authorized		16,000,000
Redeemable Preferred Shares Outstanding		15,361,787
Liquidation Preference		$ 37,790
Carrying Value		$ 37,742
Common Stock Issuable Upon Conversion		5,818,850
Preferred Shares Issued		15,361,787	9,670,730
Series D-1 Redeemable Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Redeemable Preferred Shares Authorized		3,000,000
Redeemable Preferred Shares Outstanding		2,833,334
Liquidation Preference		$ 8,500
Carrying Value		$ 8,495
Common Stock Issuable Upon Conversion		1,073,232
Preferred Shares Issued		2,833,334

Common Stock and Preferred Stock - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands			12 Months Ended
	Aug. 19, 2014	Jul. 30, 2014	Dec. 31, 2014	Dec. 31, 2012	Dec. 31, 2013
Class of Stock [Line Items]
Common stock, shares authorized			100,000,000		45,000,000
Preferred stock, shares authorized			5,000,000		0
Preferred stock, par value			$ 0.0001		$ 0.0001
Proceeds from issuance of shares			$ 69,518
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.
Common stock shares, reserved			207,402
2014 Stock Option Plan [Member]
Class of Stock [Line Items]
Common stock shares, reserved			3,196,228
Common Stock [Member]
Class of Stock [Line Items]
Number of shares issued			5,750,000	41,666
Number of common shares issued on conversion of redeemable convertible preferred stock			12,440,205
Common stock, shares authorized		100,000,000
Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, shares authorized		5,000,000
Preferred stock, par value		$ 0.0001
Over-allotment Option [Member]
Class of Stock [Line Items]
Proceeds from issuance of shares	$ 9,068
Over-allotment Option [Member] \| Common Stock [Member]
Class of Stock [Line Items]
Number of shares issued	750,000
Sale price per share	$ 13.00
IPO [Member]
Class of Stock [Line Items]
Proceeds from issuance of shares		$ 57,337
IPO [Member] \| Common Stock [Member]
Class of Stock [Line Items]
Number of shares issued		5,000,000
Sale price per share		$ 13.00
Number of common shares issued on conversion of redeemable convertible preferred stock		12,440,205

Stock-Based Awards - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
	Jan. 01, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jun. 19, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares of common stock authorized for issuance		207,402
Issuance of common stock in connection with employee stock purchase plan		$ 64
Unvested service-based stock options held by nonemployees		9,587
Aggregate intrinsic value of stock options exercised		$ 323	$ 38	$ 6
Weighted average fair value of stock option granted		$ 6.55	$ 1.51	$ 0.87
Unrecognized stock-based compensation cost		$ 4,342
Weighted average period of unrecognized stock-based compensation cost expected to be recognized		2 years 10 months 24 days
Restricted Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate intrinsic value of restricted stock award vested		$ 1,142	$ 278	$ 10
Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Issuance of common stock in connection with employee stock purchase plan,shares		5,395
2006 Stock Option Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options exercise price, description		The exercise prices, vesting and other restrictions are determined at the discretion of the board of directors, or their committee if so delegated, except that the exercise price per share of stock options may not be less than 100% of the fair market value of the share of common stock on the date of grant and the term of stock options may not be greater than ten years.
Minimum percentage of stock option exercise price at grant date fair value		100.00%
Stock options expiration period		10 years
Stock options vesting period		4 years
2006 Stock Option Plan [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options expiration period		10 years
2014 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares of common stock authorized for issuance					1,336,907
Number of shares of common stock authorized for issuance		1,292,522
2014 Stock Incentive Plan [Member] \| Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Additional number of shares authorized for issuance	790,000
2014 Stock Incentive Plan [Member] \| Scenario, Forecast [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares of common stock authorized for issuance	1,659,218
Additional number of shares of common stock , percentage	4.00%
2014 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares of common stock authorized for issuance					207,402
2014 Employee Stock Purchase Plan [Member] \| Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares of common stock authorized for issuance		202,007
Additional number of shares authorized for issuance		25,000
Issuance of common stock in connection with employee stock purchase plan,shares		5,395
Issuance of common stock in connection with employee stock purchase plan		$ 64
2014 Employee Stock Purchase Plan [Member] \| Scenario, Forecast [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Additional number of shares of common stock , percentage	0.50%

Stock-Based Awards - Schedule of Fair Value of Stock Options Weighted Average (Detail)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Risk-free interest rate	2.24%	1.23%	1.51%
Expected term (in years)	5 years 11 months 16 days	5 years 4 months 17 days	6 years 3 months
Expected volatility	76.50%	74.60%	70.00%
Expected dividend yield	0.00%	0.00%	0.00%

Stock-Based Awards - Schedule of Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Shares Issuable Under Options, Beginning balance	924,132
Shares Issuable Under Options, Granted	753,886
Shares Issuable Under Options, Exercised	(44,094)
Shares Issuable Under Options, Forfeited	(21,933)
Shares Issuable Under Options, Ending balance	1,611,991	924,132
Shares Issuable Under Options, Vested and expected to vest	1,603,423
Shares Issuable Under Options, Exercisable	651,303
Weighted Average Exercise Price, Beginning balance	$ 1.69
Weighted Average Exercise Price, Granted	9.35
Weighted Average Exercise Price, Exercised	0.78
Weighted Average Exercise Price, Forfeited	5.56
Weighted Average Exercise Price, Ending balance	5.24	$ 1.69
Weighted Average Exercise Price, Vested and expected to vest	5.26
Weighted Average Exercise Price, Exercisable	$ 1.72
Weighted Average Remaining Contractual Term, Beginning balance	6 years 6 months	7 years
Weighted Average Remaining Contractual Term, Vested and Expected to vest	6 years 6 months
Weighted Average Remaining Contractual Term, Exercisable	4 years 9 months 18 days
Aggregate Intrinsic Value, Beginning balance	$ 1,986
Aggregate Intrinsic Value, Ending balance	29,464	$ 1,986
Aggregate Intrinsic Value, Vested and Expected to vest	29,279
Aggregate Intrinsic Value, Exercisable	$ 14,196

Stock-Based Awards - Schedule of Restricted Stock Activity (Detail) - Restricted Common Stock [Member]	12 Months Ended
	Dec. 31, 2014 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested restricted common stock, Shares, Issued \| shares	123,134
Unvested restricted common stock, Shares, Vested \| shares	(94,697)
Unvested restricted common stock, Shares, Forfeited \| shares	0
Unvested restricted common stock, Shares, Ending balance \| shares	28,437
Unvested restricted common stock, Weighted Average Grant Date Fair Value, Issued \| $ / shares	$ 8.80
Unvested restricted common stock, Weighted Average Grant Date Fair Value, Vested \| $ / shares	8.80
Unvested restricted common stock, Weighted Average Grant Date Fair Value, Forfeited \| $ / shares	0
Unvested restricted common stock, Weighted Average Grant Date Fair Value, Ending balance \| $ / shares	$ 8.80

Stock-Based Awards - Schedule of Stock-Based Compensation Expense Related to Stock Options, Vesting of Restricted Common Stock and Grants of Common Stock (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 2,644	$ 476	$ 243
Research and Development Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	397	70	67
Selling and Marketing Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	68	22	28
General and Administrative Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 2,179	$ 384	$ 148

Net Loss Per Share and Unaudited Pro Forma Net Loss Per Share - Schedule of Basic and Diluted Net Loss Per Share Attributable to Common Stockholders (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Earnings Per Share [Abstract]
Net loss	$ (7,954)	$ (7,294)	$ (6,392)	$ (7,008)	$ (3,505)	$ (3,522)	$ (3,090)	$ (3,200)	$ (28,648)	$ (13,317)	$ (14,093)
Accretion of redeemable convertible preferred stock to redemption value									(11)	(27)	(35)
Net loss attributable to common stockholders	$ (7,954)	$ (7,294)	$ (6,397)	$ (7,014)	$ (3,510)	$ (3,527)	$ (3,099)	$ (3,208)	$ (28,659)	$ (13,344)	$ (14,128)
Weighted average common shares outstanding, basic and diluted									10,652,865	2,609,020	2,522,564
Net loss per share attributable to common stockholders, basic and diluted	$ (0.37)	$ (0.48)	$ (2.10)	$ (2.45)	$ (1.32)	$ (1.34)	$ (1.19)	$ (1.26)	$ (2.69)	$ (5.11)	$ (5.60)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Net Loss Per Share and Unaudited Pro Forma Net Loss Per Share - Schedule of Antidilutive Securities, Excluded from Computation of Diluted Net Loss per Share (Detail) - shares	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total options, warrants and redeemable convertible preferred stock exercisable or convertible into common stock and restricted stock	1,730,136	13,416,167	12,041,172
Equity Option [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total options, warrants and redeemable convertible preferred stock exercisable or convertible into common stock and restricted stock	1,611,991	924,132	615,377
Non Vested Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total options, warrants and redeemable convertible preferred stock exercisable or convertible into common stock and restricted stock	28,437		6,992
Series A, B, C, D and D-1 Redeemable Convertible Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total options, warrants and redeemable convertible preferred stock exercisable or convertible into common stock and restricted stock		12,440,205	11,366,973
Series A, B, C, D and D-1 Redeemable Convertible Preferred Stock [Member] \| Warrant [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total options, warrants and redeemable convertible preferred stock exercisable or convertible into common stock and restricted stock		51,830	51,830
Common Stock [Member] \| Warrant [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total options, warrants and redeemable convertible preferred stock exercisable or convertible into common stock and restricted stock	89,708

Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Thousands		12 Months Ended
	Feb. 12, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Commitments And Contingencies [Line Items]
Non-cancelable operating leases expiration		June 2017 and June 2018
Lease amendment date		Apr. 25, 2014
Lease expiration date		2017-06
Lease expiration extension date		2018-06
Rental expense		$ 649	$ 448	$ 436
Common Stock [Member]
Commitments And Contingencies [Line Items]
Common stock, shares issued	79,545
Incept [Member] \| Common Stock [Member]
Commitments And Contingencies [Line Items]
Common stock, shares issued	189,393

Commitments and Contingencies - Summary of Future Minimum Lease Payments for Operating Leases (Detail) $ in Thousands	Dec. 31, 2014 USD ($)
Commitments and Contingencies Disclosure [Abstract]
2015	$ 802
2016	820
2017	676
2018	262
Total	$ 2,560

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Contingency [Line Items]
Income tax benefit	$ 0	$ 0	$ 0
Net operating loss for federal and state income tax	15,243,000	9,204,000
Research and development tax credit carryforwards for federal and state income tax	$ 2,582,000	$ 2,005,000
Increased ownership percentage	50.00%
Unrealized net operating loss carryforwards	$ 114,000
Federal [Member]
Income Tax Contingency [Line Items]
Net operating loss for federal and state income tax	$ 39,231,000
Operating loss carryforwards,expiration period	2026
Research and development tax credit carryforwards for federal and state income tax	$ 1,784,000
Research and development tax credit carryforwards,expiration period	2026
State [Member]
Income Tax Contingency [Line Items]
Net operating loss for federal and state income tax	$ 36,923,000
Operating loss carryforwards,expiration period	2030
Research and development tax credit carryforwards for federal and state income tax	$ 1,208,000
Research and development tax credit carryforwards,expiration period	2024

Income Taxes - Reconciliation of Federal Income Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Federal statutory income tax rate	(34.00%)	(34.00%)	(34.00%)
Federal and state research and development tax credit	(2.50%)	(6.60%)	(1.20%)
State taxes, net of federal benefit	(4.60%)	(4.80%)	(5.10%)
Stock-based compensation	1.60%	1.30%	0.30%
Other	0.80%
Change in deferred tax asset valuation allowance	38.70%	44.10%	40.00%
Effective income tax rate	0.00%	0.00%	0.00%

Income Taxes - Net Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Tax Disclosure [Abstract]
Net operating loss carryforwards	$ 15,243	$ 9,204
Research and development tax credit carryforwards	2,582	2,005
Capitalized start-up costs	2,204	2,426
Capitalized research and development expenses, net	15,746	11,571
Accrued expenses and other temporary differences	1,050	570
Total gross deferred tax assets	36,825	25,776
Valuation allowance	(36,825)	(25,776)	$ (19,815)	$ (14,171)
Net deferred tax assets	$ 0	$ 0

Income Taxes - Changes in Valuation Allowance for Deferred Tax Assets (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Valuation allowance as of beginning of year	$ 25,776	$ 19,815	$ 14,171
Decreases recorded as benefit to income tax provision	0	0	0
Increases recorded to income tax provision	11,049	5,961	5,644
Valuation allowance as of end of year	$ 36,825	$ 25,776	$ 19,815

401(k) Savings Plan - Additional Information (Detail)	12 Months Ended
401(k) Savings Plan - Additional Information (Detail)	Dec. 31, 2014 USD ($)
Postemployment Benefits [Abstract]
Contributions to savings plan	$ 0

Related Party Transactions - Additional Information (Detail) - USD ($) $ in Thousands		12 Months Ended
	Feb. 12, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Common Stock [Member]
Related Party Transaction [Line Items]
Common stock, shares issued	79,545
Research and Development Expense [Member]
Related Party Transaction [Line Items]
Fair value of shares issued		$ 1,665
Research and Development Expense [Member] \| Common Stock [Member]
Related Party Transaction [Line Items]
Common stock, shares issued		189,393
General and Administrative Expense [Member]
Related Party Transaction [Line Items]
Fair value of shares issued	$ 699	$ 699
General and Administrative Expense [Member] \| Common Stock [Member]
Related Party Transaction [Line Items]
Common stock, shares issued		79,545
Receivables [Member]
Related Party Transaction [Line Items]
Invoiced consulting and other services		$ 82	$ 232	$ 366
Payables [Member] \| Legal Fees [Member]
Related Party Transaction [Line Items]
Invoiced consulting and other services		27	0	0
Payables [Member] \| Consultant Fees [Member]
Related Party Transaction [Line Items]
Invoiced consulting and other services		$ 0	$ 14	$ 0
Incept [Member] \| Common Stock [Member]
Related Party Transaction [Line Items]
Common stock, shares issued	189,393
Incept [Member] \| Research and Development Expense [Member]
Related Party Transaction [Line Items]
Fair value of shares issued	$ 1,665

Selected Quarterly Financial Data (Unaudited) - Schedule of Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Statements of Operations Data:
Revenue	$ 505	$ 143	$ 97	$ 27					$ 772		$ 10
Loss from operations	(7,547)	(6,776)	(5,946)	(6,825)	$ (3,419)	$ (3,435)	$ (2,989)	$ (3,060)	(27,094)	$ (12,903)	(13,671)
Net loss	(7,954)	(7,294)	(6,392)	(7,008)	(3,505)	(3,522)	(3,090)	(3,200)	(28,648)	(13,317)	(14,093)
Net loss attributable to common stockholders	$ (7,954)	$ (7,294)	$ (6,397)	$ (7,014)	$ (3,510)	$ (3,527)	$ (3,099)	$ (3,208)	$ (28,659)	$ (13,344)	$ (14,128)
Basic and diluted net loss attributable to common stockholders per share	$ (0.37)	$ (0.48)	$ (2.10)	$ (2.45)	$ (1.32)	$ (1.34)	$ (1.19)	$ (1.26)	$ (2.69)	$ (5.11)	$ (5.60)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Selected Quarterly Financial Data (Unaudited) - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Collaboration revenue	$ 312	$ 312