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Document and Entity Information - USD ($)	12 Months Ended
Document and Entity Information - USD ($)	Dec. 31, 2015	Mar. 01, 2016	Jun. 30, 2015
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2015
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	FY
Trading Symbol	CERU
Entity Registrant Name	CERULEAN PHARMA INC.
Entity Central Index Key	0001401914
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		27,363,965
Entity Public Float			$ 92,191,525.60

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 75,908	$ 51,174
Accounts receivable, prepaid expenses, and other current assets	1,394	1,662
Total current assets	77,302	52,836
Property and equipment, net	576	342
Other assets	347	215
Total	78,225	53,393
Current liabilities:
Current portion of loan payable	7,652	3,124
Accounts payable	2,226	1,255
Accrued expenses	6,459	3,648
Other liabilities		34
Total current liabilities	16,337	8,061
Long-term liabilities:
Loan payable, net of current portion	12,672
Other long-term liabilities	473	7
Total long-term liabilities	13,145	7
Commitments (Note 12)
Stockholders’ equity:
Preferred stock, $0.01 par value; 5,000,000 shares authorized, no shares issued or outstanding
Common stock, $0.0001 par value; 120,000,000 shares authorized, 27,346,780 and 20,125,049 shares issued and outstanding at December 31, 2015 and 2014, respectively	3	2
Additional paid-in capital	210,115	167,104
Accumulated deficit	(161,375)	(121,781)
Total stockholders’ equity	48,743	45,325
Total	$ 78,225	$ 53,393

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2015	Dec. 31, 2014
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	120,000,000	120,000,000
Common stock, shares issued	27,346,780	20,125,049
Common stock, shares outstanding	27,346,780	20,125,049

Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Statement [Abstract]
Revenue							$ 33	$ 47		$ 80	$ 6
Operating expenses:
Research and development	$ 7,157	$ 7,092	$ 6,678	$ 5,021	$ 4,701	$ 2,928	2,648	1,495	$ 25,948	11,772	9,700
General and administrative	2,872	2,954	2,717	2,681	2,607	2,441	2,029	1,510	11,224	8,587	6,166
Total operating expenses	10,029	10,046	9,395	7,702	7,308	5,369	4,677	3,005	37,172	20,359	15,866
Other income (expense):
Interest income	2	4	1	3	4	2	2	1	10	9	2
Interest expense	(689)	(509)	(513)	(721)	(163)	(191)	(268)	(461)	(2,432)	(1,083)	(1,487)
Loss on extinguishment of debt							(2,493)			(2,493)
Decrease in value of preferred stock warrant liability								504		504	202
Total other income (expense), net	(687)	(505)	(512)	(718)	(159)	(189)	(2,759)	44	(2,422)	(3,063)	(1,283)
Net loss attributable to common stockholders	$ (10,716)	$ (10,551)	$ (9,907)	$ (8,420)	$ (7,467)	$ (5,558)	$ (7,403)	$ (2,914)	$ (39,594)	$ (23,342)	$ (17,143)
Net loss per share attributable to common stockholders:
Basic and diluted	$ (0.39)	$ (0.39)	$ (0.37)	$ (0.41)	$ (0.37)	$ (0.28)	$ (0.44)	$ (3.70)	$ (1.56)	$ (1.60)	$ (25.05)
Weighted-average common shares outstanding:
Basic and diluted	27,346,780	27,307,103	26,690,673	20,350,557	20,125,009	20,124,574	16,883,716	786,986	25,431,332	14,548,516	684,330

Consolidated Statement of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Term Loan Facility [Member]	IPO [Member]	Follow-on Offering [Member]	Private Placement [Member]	Redeemable Convertible Preferred Stock [Member]	Common Stock [Member]	Common Stock [Member] IPO [Member]	Common Stock [Member] Follow-on Offering [Member]	Common Stock [Member] Private Placement [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member] Term Loan Facility [Member]	Additional Paid-in Capital [Member] IPO [Member]	Additional Paid-in Capital [Member] Follow-on Offering [Member]	Additional Paid-in Capital [Member] Private Placement [Member]	Accumulated Deficit [Member]
Beginning balance at Dec. 31, 2012	$ (80,039)										$ 1,257					$ (81,296)
Redeemable convertible preferred stock, Beginning balance at Dec. 31, 2012						$ 83,751
Beginning balance, shares at Dec. 31, 2012							609,945
Redeemable convertible preferred stock, Beginning balance, shares at Dec. 31, 2012						87,037,546
Exercise of stock options	35										35
Exercise of stock options, shares							8,911
Stock-based compensation	622										622
Conversion of convertible preferred stock into common stock	2,226					$ (2,226)					2,226
Conversion of convertible preferred stock into common stock, shares						(1,830,190)	166,675
Net loss	(17,143)															(17,143)
Ending balance at Dec. 31, 2013	(94,299)										4,140					(98,439)
Redeemable convertible preferred stock, Ending balance at Dec. 31, 2013						$ 81,525
Ending balance, shares at Dec. 31, 2013							785,531
Redeemable convertible preferred stock, Ending balance, shares at Dec. 31, 2013						85,207,356
Exercise of stock options	140										140
Exercise of stock options, shares							41,566
Stock-based compensation	885										885
Issuance of Common Stock			$ 59,862					$ 1					$ 59,861
Issuance of Common Stock, shares								9,569,715
Conversion of convertible preferred stock into common stock	81,526					$ (81,525)	$ 1				81,525
Conversion of convertible preferred stock into common stock, shares						(85,207,356)	6,826,004
Reclassification/Issuance of warrants			$ 424										$ 424
Conversion of convertible notes	20,129										20,129
Conversion of convertible notes, shares							2,902,233
Net loss	(23,342)															(23,342)
Ending balance at Dec. 31, 2014	45,325						$ 2				167,104					(121,781)
Ending balance, shares at Dec. 31, 2014							20,125,049
Exercise of stock options	$ 1,628										1,628
Exercise of stock options, shares	370,230						370,230
Stock-based compensation	$ 2,375										2,375
Issuance of Common Stock				$ 37,185	$ 1,000				$ 1					$ 37,184	$ 1,000
Issuance of Common Stock, shares									6,716,000	135,501
Reclassification/Issuance of warrants		$ 824										$ 824
Net loss	(39,594)															(39,594)
Ending balance at Dec. 31, 2015	$ 48,743						$ 3				$ 210,115					$ (161,375)
Ending balance, shares at Dec. 31, 2015							27,346,780

Consolidated Statement of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Preferred stock, par value	$ 0.01	$ 0.01
Common stock, par value	$ 0.0001	$ 0.0001
Stock issuance costs		$ 187
IPO [Member]
Stock issuance costs		$ 7,126
Follow-on Offering [Member]
Stock issuance costs	$ 3,111
Minimum [Member]
Conversion price, per share			$ 14.51
Maximum [Member]
Conversion price, per share			$ 39.21

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash flows from operating activities:
Net loss	$ (39,594)	$ (23,342)	$ (17,143)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	2,375	885	622
Noncash rent expense	(41)	29	(1)
Change in carrying value of preferred stock warrant liability		(504)	(202)
Depreciation and amortization	192	126	197
(Gain) loss on disposal of property and equipment	(6)	(28)	7
Loss on extinguishment of debt		2,493
Amortization of debt discount and deferred financing costs	739	215	215
Changes in operating assets and liabilities:
Accounts receivable, prepaid expenses and other current assets	342	(695)	(209)
Accounts payable	795	341	14
Accrued expenses	3,283	1,419	(114)
Net cash used in operating activities	(31,915)	(19,061)	(16,614)
Cash flows from investing activities:
Purchases of property and equipment	(277)	(225)	(7)
Proceeds from sale of property and equipment	23	40
Increase in restricted cash	(230)
Net cash used in investing activities	(484)	(185)	(7)
Cash flows from financing activities:
Proceeds from sale of common stock	2,628	140	35
Proceeds from public stock offering, net	37,185	59,862
Proceeds from loan payable	21,000
Proceeds from issuance of convertible promissory notes		8,500	8,824
Payments on loan payable	(3,321)	(3,348)	(3,084)
Cash paid for debt issuance costs	(359)	(222)	(373)
Net cash provided by financing activities	57,133	64,932	5,402
Net increase (decrease) in cash and cash equivalents	24,734	45,686	(11,219)
Cash and cash equivalents — Beginning of year	51,174	5,488	16,707
Cash and cash equivalents — End of year	75,908	51,174	5,488
Supplemental disclosures of noncash investing and financing activities:
Purchase of property and equipment in accounts payable	177
Conversion of redeemable convertible preferred stock into common stock		81,526	2,226
Conversion of convertible notes and accrued interest into common stock, net		20,129
Reclassification of warrants to additional paid-in capital		424
Warrants issued with term loan facility	824
Supplemental cash flow information — Interest paid	$ 1,000	$ 400	$ 664

Nature of Business and Operations

12 Months Ended

Dec. 31, 2015

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Nature of Business and Operations

1.	NATURE OF BUSINESS AND OPERATIONS

Nature of Business — Cerulean Pharma Inc. (the “Company”) was incorporated on November 28, 2005, as a Delaware corporation and is located in Waltham, Massachusetts. The Company was formed to develop novel, nanotechnology-based therapeutics in the areas of oncology and other diseases. In 2013, the Company formed a wholly-owned subsidiary, Cerulean Pharma Australia Pty Ltd as an Australian-based proprietary limited company to perform clinical activities in Australia.

The Company's operations to date have consisted primarily of raising capital, product research and development, and initial market development.

The Company has not generated any revenue related to its primary business purpose to date and is subject to a number of risks similar to those of other development stage life science companies, including dependence on key individuals, competition from other companies, the need for development of commercially viable products, and the need to obtain adequate additional financing to fund the development of its product candidates. The Company is also subject to a number of risks similar to other companies in the industry, including rapid technological change, regulatory approval of products, uncertainty of market acceptance of products, competition from substitute products and larger companies, the need to obtain additional financing, compliance with government regulations, protection of proprietary technology, dependence on third parties, product liability and dependence on key individuals.

The Company has an accumulated deficit of $161.4 million at December 31, 2015. The Company has financed its operations primarily through private placements of its preferred stock, proceeds from borrowings, an initial public offering completed in 2014 and a follow-on offering completed in 2015. The Company has not completed development of any product candidate and has devoted substantially all of its financial resources and efforts to research and development, including preclinical and clinical development. Accordingly, the Company will continue to depend on its ability to raise capital through equity and debt issuances and/or through strategic partnerships. The Company expects to continue to incur significant expenses and increasing operating losses for at least several years. The Company believes that its cash and cash equivalents as of December 31, 2015, will be able to fund operating expenses, debt service and capital expenditure requirements for at least twelve months from our 2015 financial statement issuance date.

Follow-on Offering — On April 10, 2015, the Company completed the issuance and sale of 6,716,000 shares of common stock in an underwritten public offering at a price to the public of $6.00 per share. The sale of shares of common stock included 876,000 shares sold pursuant to the full exercise of the underwriters’ option to purchase additional shares of common stock. The net proceeds to the Company from this offering were $37.2 million after deducting underwriting discounts and commissions and offering expenses payable by the Company.

Initial Public Offering — On April 15, 2014, the Company completed the sale of 8,500,000 shares of its common stock in its initial public offering (the “IPO”), at a price to the public of $7.00 per share. On May 7, 2014, the Company completed the sale of an additional 1,069,715 shares of common stock at a price to the public of $7.00 per share under a partial exercise by the underwriters of their option to purchase additional shares of common stock. The sale of shares to the public resulted in net proceeds of $59.9 million after deducting underwriting discounts and commissions and offering expenses payable by the Company.

In connection with the closing of the IPO, all of the Company’s outstanding redeemable convertible preferred stock and convertible notes automatically converted into shares of common stock as of April 15, 2014, resulting in the issuance by the Company of an additional 9,728,237 shares of common stock.

In connection with the completion of the IPO on April 15, 2014, the Company’s outstanding warrants to purchase 1,857,226 shares of the Company’s preferred stock automatically converted into warrants to purchase an aggregate of 128,663 shares of the Company’s common stock and, as a result, the Company reclassified the warrant liability to additional paid-in capital.

Significant Accounting Policies

12 Months Ended

Dec. 31, 2015

Accounting Policies [Abstract]

Significant Accounting Policies

2.	SIGNIFICANT ACCOUNTING POLICIES

Use of Estimates — The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and 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 period.

On an ongoing basis, the Company's management evaluates its estimates, including estimates related to clinical trial accruals, stock-based compensation expense, and reported amounts of revenues and expenses during the reported period. The Company bases its estimates on historical experience and other market-specific or other relevant assumptions that it believes to be reasonable under the circumstances. Although the Company regularly assesses these estimates, actual results could differ from those estimates. Changes in estimates are recorded in the period in which they become known.

Principles of Consolidation — The consolidated financial statements include the accounts of the Company and its wholly-owned subsidiary. All intercompany accounts and transactions have been eliminated.

Segment Information — Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision-maker in making decisions regarding resource allocation and assessing performance. The Company views its operations and manages its business in one operating segment; however, the Company operates in two geographic regions: United States (Waltham, MA) and Australia (Sydney, NSW). There is no revenue generated or long-lived assets located within the Australian location.

Cash and Cash Equivalents — Cash equivalents include all highly liquid investments maturing within 90 days from the date of purchase and consist primarily of money market funds.

Concentrations of Credit Risk — Financial instruments that subject the Company to significant concentrations of credit risk consist primarily of cash and cash equivalents. Substantially all of the Company’s cash and cash equivalents are held at one financial institution that management believes to be of high-credit quality. Deposits with this financial institution may exceed the amount of insurance provided on such deposits; however these deposits may be redeemed upon demand and, therefore, bear minimal risk.

Restricted Cash — At December 31, 2015 and 2014, the Company had restricted cash of $347,000 and $117,000, respectively. The restricted cash balances were used to collateralize stand-by letters of credit issued by the Company as a security deposit for its current and former facility leases. The balance at December 31, 2014, was with respect to the Company’s former facility lease that was scheduled to expire in February 2016 and was terminated early on December 31, 2015. The balance at December 31, 2015, includes the balance for the former facility lease and the Company’s new facility lease which is scheduled to expire in February 2021. The restricted cash is included within other assets in the balance sheet.

Property and Equipment — Property and equipment are recorded at cost and depreciated over their estimated useful lives using the straight-line method. Repairs and maintenance costs are expensed as incurred, whereas major improvements are capitalized as additions to property and equipment.

Depreciation is provided using the straight-line method over the following estimated useful lives:

Laboratory equipment		5 years
Computer equipment		3 years
Office furniture and equipment		5 years
Leasehold improvements		Lesser of useful life or remaining lease term

Impairment of Long-Lived Assets — Long-lived assets are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of the asset may not be recoverable. When such events occur, the Company compares the carrying amounts of the assets to their undiscounted expected future cash flows. If this comparison indicates that there is impairment, the amount of impairment is calculated as the difference between the carrying value and fair value. For the years ended December 31, 2015 and 2014, the Company has not recorded an impairment charge for its long-lived assets.

Revenue Recognition — The Company’s revenue to date has been insignificant and has been generated from short-term research agreements with pharmaceutical companies and federal grants. There have been no multiple element arrangements. Revenue is recognized when four basic criteria are met: (1) persuasive evidence of an arrangement exists, (2) delivery has occurred or services have been rendered, (3) the fee is fixed or determinable, and (4) collectability is reasonably assured. Accordingly, the Company has recognized revenue under its agreements as the services were performed.

Comprehensive Loss — Comprehensive loss consists of net loss and changes in equity during a period from transactions and other equity and circumstances generated from non-owner sources. The Company had no items of comprehensive loss, other than its net loss, for each of the periods presented.

Research and Development Costs — Research and development expenses consist of expenses incurred in performing research and development activities, including compensation and benefits for full-time research and development employees, an allocation of facilities expenses, overhead expenses, manufacturing process-development and scale-up activities, clinical trial and related clinical manufacturing expenses, fees paid to clinical research organizations, or CROs, and investigative sites, payments to universities under the Company’s license agreements and other outside expenses. In the early phases of development, the Company’s research and development costs are often devoted to expanding its product platform and are not necessarily allocable to a specific target. Research and development costs are expensed as incurred. Nonrefundable advanced payments, if any, for goods and services used in research and development are recognized as an expense as the related goods are delivered or services are performed.

Preferred Stock Warrant Liability — Freestanding warrants related to shares that are redeemable or contingently redeemable are classified as a liability on the Company’s balance sheets. The Company uses the Black-Scholes option-pricing model to estimate the fair value of the warrants. Changes in the fair value of these warrants are recorded in the statements of operations. All of the Company’s warrants to purchase preferred stock were converted to warrants to purchase common stock upon the Company’s IPO in April 2014. Accordingly, the preferred stock warrant liability was reclassified to additional paid-in capital.

Redeemable Convertible Preferred Stock — The Company classified redeemable convertible preferred stock that was redeemable outside of the Company’s control outside of permanent equity. The Company recorded such redeemable preferred stock at fair value upon issuance, net of any issuance costs or discounts, and the carrying value was being increased by periodic accretion to its redemption value. In the absence of retained earnings these accretion charges were recorded against additional paid-in capital, if any, and then to accumulated deficit. The Company amortized the accretion using the interest method. All of the Company’s redeemable convertible preferred stock was automatically converted to common stock in connection with the IPO.

Stock-Based Compensation — The Company accounts for stock-based awards at fair value, which is measured using the Black-Scholes option-pricing model. The fair value measurement date for employee awards is generally the date of grant. The fair value measurement date for nonemployee awards is generally the date the performance of services is completed. Stock-based compensation costs are recognized as an expense over the requisite service period, which is generally the vesting period, on a straight-line basis for all time-vested awards. The Company issued performance based grants where the vesting of the grant is tied to certain milestone performance and in these cases, the compensation is recognized as expense when the probability of the milestone is met.

Stock-based awards to nonemployees are remeasured at each reporting date and recognized as services are rendered, generally on a straight-line basis. The Company believes that the fair value of these awards is more reliably measurable than the fair value of the services rendered. Stock-based compensation is classified in the accompanying consolidated statements of operations in the department where the related services are provided.

Net Loss per Share Attributable to Common Stockholders — Basic net loss attributable to common stockholders per share is computed by dividing the net loss attributable to common stockholders by the weighted-average number of common shares outstanding for the period. During periods where the Company might earn net income, the Company would allocate participating securities a proportional share of net income determined by dividing total weighted average participating securities by the sum of the total weighted average common shares and participating securities (the “two-class method”). Participating securities have the effect of diluting both basic and diluted earnings per share during periods of income. During periods where the Company incurred net loss, the Company allocates no loss to participating securities because they have no contractual obligation to share in the losses of the Company. The Company computes diluted loss per common share after giving consideration to the dilutive effect of stock options and warrants that are outstanding during the period, except where such nonparticipating securities would be antidilutive.

Income Taxes — Deferred income taxes are provided for the temporary differences arising between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes and for operating loss carryforwards and credits. Deferred tax assets and liabilities are recorded using tax rates expected to be in effect in the year in which the differences are expected to reverse. A valuation allowance is provided for any net deferred tax assets for which management believes it is more likely than not that the net deferred tax assets will not be realized.

The Company provides reserves for potential payment of tax to various tax authorities related to uncertain tax positions. The tax benefits recorded are based on a determination of whether and how much of a tax benefit taken by the Company in its filings or positions is “more likely than not” to be realized following resolution of any uncertainty related to the tax benefit, assuming the matter in question will be raised by the tax authorities. Potential interest and penalties associated with such uncertain tax positions are recorded as a component of income tax expense. At December 31, 2015 and 2014, the Company has not identified any significant uncertain tax positions.

Guarantees and Indemnification — As permitted under Delaware law, the Company indemnifies its officers and directors employees for certain events or occurrences while the officer or director is, or was serving at the Company’s request in such a capacity. The term of the indemnification is for the officer’s or director’s lifetime.

Recent Accounting Pronouncements — On February 25, 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update 2016-02, “Leases” (“ASU 2016-02”), which provides new accounting guidance on leases. ASU 2016-02 is effective for fiscal years beginning after December 15, 2018. The Company has not yet evaluated the impact of adoption of this new guidance.

In November 2015, the FASB issued Accounting Standards Update 2015-17, “Balance Sheet Classification of Deferred Taxes” (“ASU 2015-17”). To simplify the presentation of deferred taxes assets and liabilities, the new guidance requires that all deferred tax assets and liabilities, along with any related valuation allowance, be classified as noncurrent on the balance sheet. ASU 2015-17 is effective for public business entities in fiscal years beginning after December 15, 2016 and is not expected to have a material impact on the Company’s consolidated financial statements.

In April 2015, the FASB issued Accounting Standards Update 2015-03, “Simplifying the Presentation of Debt Issuance Costs” (“ASU 2015-03”). To simplify presentation of debt issuance costs, ASU 2015-03 requires that debt issuance costs related to a recognized debt liability be presented in the balance sheet as a direct deduction from the carrying amount of that debt liability, consistent with debt discounts. ASU 2015-03 is effective for annual and interim reporting periods beginning January 1, 2016, and early adoption is permitted. The Company retrospectively adopted the guidance for its year ended December 31, 2015 and as a result, reclassified approximately $0.2 million in deferred financing costs that would have appeared as “Other assets” to “Long-term loan payable” in its accompanying consolidated balance sheet. The impact to prior years was not material.

Net Loss Per Share Attributable to Common Stockholders

12 Months Ended

Dec. 31, 2015

Earnings Per Share [Abstract]

Net Loss Per Share Attributable to Common Stockholders

3.	NET LOSS PER SHARE ATTRIBUTABLE TO COMMON STOCKHOLDERS

The following table summarizes the computation of basic and diluted net loss per share attributable to common stockholders of the Company (in thousands, except share data and per share data):

	Years Ended December 31,
	2015			2014			2013
Net loss attributable to common stockholders — basic and diluted	$	(39,594	)	$	(23,342	)	$	(17,143	)
Weighted-average number of common shares — basic and diluted		25,431,332			14,548,516			684,330
Net loss per share attributable to common stockholders — basic and diluted	$	(1.56	)	$	(1.60	)	$	(25.05	)

The Company has reported a net loss for all periods presented, therefore diluted net loss per common share is the same as basic net loss per common share.

The following potentially dilutive securities outstanding have been excluded from the computation of diluted weighted-average shares outstanding, because such securities had an antidilutive impact due to the losses reported (in common stock equivalent shares):

	As of December 31,
	2015		2014		2013
Options to purchase common stock		3,454,926		2,126,176		1,062,694
Warrants to purchase redeemable convertible preferred stock		—		—		128,663
Warrants to purchase common stock		300,564		128,663		—
Redeemable convertible preferred stock		—		—		6,826,004
Convertible notes payable		—		—		754,785

Property and Equipment

12 Months Ended

Dec. 31, 2015

Property Plant And Equipment [Abstract]

Property and Equipment

4.	PROPERTY AND EQUIPMENT

Property and equipment consist of the following (in thousands):

	As of December 31,
	2015			2014
Laboratory equipment	$	1,314		$	1,163
Computer equipment		350			260
Office furniture and equipment		25			292
Leasehold improvements		33			117
		1,722			1,832
Less accumulated depreciation and amortization		(1,146	)		(1,490	)
Property and equipment, net	$	576		$	342

Depreciation and amortization expense for the years ended December 31, 2015, 2014, and 2013 was $192,000, $126,000, and $197,000, respectively.

Accrued Expenses

12 Months Ended

Dec. 31, 2015

Payables And Accruals [Abstract]

Accrued Expenses

5.	ACCRUED EXPENSES

Accrued expenses consist of the following (in thousands):

	As of December 31,
	2015		2014
Accrued clinical trial costs	$	2,631	$	848
Accrued contract manufacturing expenses		945		580
Accrued compensation and benefits		1,864		983
Accrued interest		136		574
Other accrued expenses		883		663
Total accrued expenses	$	6,459	$	3,648

Convertible Notes Payable to Shareholders

12 Months Ended

Dec. 31, 2015

Debt Disclosure [Abstract]

Convertible Notes Payable to Shareholders

6.	CONVERTIBLE NOTES PAYABLE TO SHAREHOLDERS

In May 2010 and September 2010, the Company issued one-year convertible notes payable in the amounts of $5,000,000 and $1,500,000, respectively, to existing investors, with a stated interest rate of 7%. In November 2010, the principal and accrued interest of $176,000 were converted into 9,021,175 shares of Series C Preferred Stock at $0.74 per share. The Company also provided for the issuance of seven-year warrants to purchase Series C Preferred Stock with the notes. The issuance of the warrants was contingent upon the conversion of the notes to Series C Preferred Stock. The number of shares included in the warrants was determined by dividing 10% of the note principal converted to Series C Preferred Stock by the Series C Preferred Stock per share issue price. Concurrent with the conversion of the notes, warrants to purchase 878,370 shares of Series C Preferred Stock at $0.74 per share became exercisable. The Company estimated the fair value of the warrants on the issue date to be $474,000 using the Black-Scholes option-pricing model with the following assumptions: volatility of 80%, contractual term of seven years, risk-free interest rate of 1.85%, and no dividend yield. The Company determined the fair value of the warrants at the end of each subsequent reporting period using the Black-Scholes option-pricing model (see Note 10) until their conversion to warrants to purchase 60,532 shares of common stock upon the IPO in April 2014.

In August 2013, the Company issued convertible promissory notes in the amount of $8,824,000 to existing investors, with a stated interest rate of 7%. Outstanding principal and unpaid accrued interest due under the notes were automatically converted into shares of the Company’s common stock upon the closing of the Company’s IPO in April 2014.

In February and March 2014, the Company issued convertible promissory notes in the aggregate amount of $6,000,000 to existing investors and a convertible promissory note in the amount of $2,500,000 to a new investor. All the notes had a stated interest rate of 7%. Outstanding principal and unpaid accrued interest due under the notes were automatically converted into shares of the Company’s common stock upon the closing of the Company’s IPO in April 2014, at a conversion price equal to 77.5% of the IPO price. The Company recorded a loss on the extinguishment of the notes of $2,493,000 in April 2014, equal to the difference between the fair value of the shares into which the notes converted and the carrying amount of the notes upon the closing of the Company’s IPO.

Loan Agreements

12 Months Ended

Dec. 31, 2015

Debt Disclosure [Abstract]

Loan Agreements

7.	LOAN AGREEMENTS

On January 8, 2015 (the “Closing Date”), the Company entered into a term loan facility of up to $26.0 million (the “Term Loan”) with Hercules Technology Growth Capital, Inc. (“Hercules”). The proceeds were used to repay the Company’s existing term loan facility with Lighthouse Capital Partners VI, L.P. (“Lighthouse Capital”) and for general corporate and working capital purposes. At December 31, 2015, the Company had $21.0 million in principal outstanding under the Term Loan.

The Term Loan is governed by a loan and security agreement, dated January 8, 2015, between the Company and Hercules (the “Hercules Loan Agreement”). The Hercules Loan Agreement provided for up to three separate borrowings, the first of which was funded in the amount of $15.0 million on the Closing Date. On November 24, 2015, the Company drew a second tranche in the amount of $6.0 million. The Company elected not to commence a randomized Phase 2 clinical study of CRLX101 in combination with chemoradiotherapy on or prior to December 15, 2015, which was a condition of obtaining an additional tranche in an amount of up to $5.0 million. As a result, the Company is no longer eligible to borrow this amount under the Term Loan.

The Term Loan will mature on July 1, 2018. Each advance under the Term Loan accrues interest at a floating per annum rate equal to the greater of (i) 7.30% or (ii) the sum of 7.30% plus the prime rate minus 5.75%. The Term Loan provided for interest-only payments on a monthly basis until December 31, 2015. Thereafter, payments will be payable monthly in equal installments of principal and interest to fully amortize the outstanding principal over the remaining term of the loan, subject to recalculation upon a change in the prime rate. The Company may prepay the Term Loan in whole or in part upon seven business days’ prior written notice to Hercules. Any such prepayment of the Term Loan is subject to a prepayment charge of 2.0% if such prepayment occurs after twelve months following the Closing Date but on or prior to twenty-four months following the Closing Date and 1.0% thereafter. Amounts outstanding during an event of default are payable upon Hercules’ demand and shall accrue interest at an additional rate of 5.0% per annum of the past due amount outstanding. The minimum future principal payments are as follows (in thousands):

Year Ending December 31,
2016	$	7,945
2017		8,544
2018		4,511
Unamortized discount relating to warrants and deferred financing costs		(676	)
Total		20,324
Less current portion		(7,652	)
Long-term portion	$	12,672

At the end of the loan term (whether at maturity, by prepayment in full or otherwise), the Company shall pay a final end of term charge to Hercules in the amount of 6.7% of the aggregate original principal amount advanced by Hercules. The amount of the end of term charge is being accrued over the loan term as interest expense.

In connection with the Hercules Loan Agreement, the Company issued to Hercules a warrant to purchase shares of the common stock of the Company at an exercise price of $6.05 per share. The warrant is exercisable for 171,901 shares of common stock. The warrant is exercisable until January 8, 2020. The Company estimated the fair value of the warrant for shares exercisable on the issue date in January 2015 to be $824,000. The value of the warrant was recorded as a discount to the loan. The fair value of the warrant was estimated on the date of issue for the exercisable shares at that date using the Black-Scholes option-pricing model. The following table shows the Black-Scholes assumptions used to value the warrant:

	January 8, 2015
Contractual life	5 years
Volatility rate		61	%
Risk-free interest rate		1.5	%
Expected dividends		—

At December 31, 2015, the Company’s balance of unamortized deferred financing costs and unamortized debt discount were $0.2 million and $0.5 million, respectively. These costs are being amortized to interest expense using the effective interest method over the term of the loan.

In connection with the Hercules Loan Agreement, the Company entered into a stock purchase agreement with Hercules, whereby Hercules purchased 135,501 shares of common stock from the Company at a price per share of $7.38, which was equal to the closing price of the common stock on the NASDAQ Global Market on January 7, 2015, for an aggregate purchase price of approximately $1.0 million.

In December 2011, the Company entered into a loan and security agreement with Lighthouse Capital to borrow up to $10.0 million in one or more advances by December 31, 2012. In both March 2012 and August 2012, the Company borrowed $5.0 million under the loan and security agreement, for a total of $10.0 million. This amount was being repaid over 36 months beginning on December 1, 2012, at an interest rate of 8.25%. In addition, the Company was required to make an additional payment in the amount of $600,000 at the end of the loan term. The amount was accrued over the loan term as interest expense. The amount accrued as of December 31, 2014 was $574,000, and it was included in accrued expense in the Company’s consolidated balance sheet. In January 2015, the Company repaid in full the amount outstanding under the Lighthouse Capital agreement, or $3.6 million, with the proceeds from the Hercules Loan Agreement.

In connection with the loan and security agreement with Lighthouse Capital, the Company issued Lighthouse Capital a warrant to purchase a maximum of 66,436 shares of the Company’s Series D Preferred Stock, at an exercise price of $12.04 per share and with an expiration date 10 years from the date of issue (December 2021). The Company determined the fair value of the warrant at the end of each reporting period using the Black-Scholes option pricing model until the warrant converted to a warrant to purchase 66,436 shares of common stock upon the completion of the IPO. The value of the warrant was recorded as a discount to the loan and was being amortized as interest expense using the effective interest method over the 36-month repayment term. The unamortized discount relating to the warrants, or $0.2 million, was expensed as interest expense upon repayment of the loan in January 2015.

Stockholder's Equity

12 Months Ended

Dec. 31, 2015

Stockholders Equity Note [Abstract]

Stockholder's Equity (Deficit)

8.	STOCKHOLDERS’ EQUITY

Common Stock — As discussed in Note 1, in April 2015, the Company issued 6,716,000 shares of common stock in connection with an underwritten public offering and during 2014 the Company issued 19,297,952 shares of common stock in connection with its IPO, the conversion of preferred stock and convertible notes into common stock, and the partial exercise of the underwriters’ overallotment option in the IPO.

Reserved Shares of Common Stock — The Company has reserved the following number of shares of common stock at December 31, 2015 and 2014:

	As of December 31,
	2015		2014
Warrants to purchase common stock		300,564		128,663
Common stock options		3,995,876		3,561,104
Total		4,296,440		3,689,767

- 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
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-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
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-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
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-Subparagraph (SAB TOPIC 4.C)
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Reference 7: http://www.xbrl.org/2003/role/presentationRef
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Reference 8: http://www.xbrl.org/2003/role/presentationRef
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-Paragraph 1
-Subparagraph (SX 210.3-04)
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Reference 9: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
-Topic 505
-SubTopic 30
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-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
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-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 Staff Accounting Bulletin (SAB)
-Number Topic 4
-Section E

Reference 15: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Staff Accounting Bulletin (SAB)
-Number Topic 4
-Section C

+ Details

Stock Option Plans

12 Months Ended

Dec. 31, 2015

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock Option Plans

9.	STOCK OPTION PLANS

2007 Stock Incentive Plan – The Company’s 2007 Incentive Stock Plan, or the 2007 Plan, provides for the grant of qualified incentive stock options and nonqualified stock options or other awards to the Company’s employees, officers, directors, advisors, and outside consultants to purchase up to an aggregate of 1,275,211 shares of the Company’s common stock, as amended in January 2014. The stock options generally vest over a four-year period and expire 10 years from the date of grant. Certain options provide for accelerated vesting if there is a change in control, as defined in the 2007 Plan. Effective with the IPO, no additional grants will be issued from the 2007 Plan and all shares available for grant under the 2007 Plan were transferred to the 2014 Plan. Accordingly, at December 31, 2015 and 2014, there were no shares available for future grant under the 2007 Plan.

Prior to the IPO, in determining the exercise prices for options granted, the Company’s board of directors considered the fair value of the common stock as of the measurement date. The fair value of the common stock was determined by the board of directors at each award grant date based upon a variety of factors, including the results obtained from a common stock valuation, the Company’s financial position and historical financial performance, the status of technological developments within the Company’s products, the composition and ability of the current research and management team, an evaluation or benchmark of the Company’s competition, the current business climate in the marketplace, the illiquid nature of the common stock, arm’s-length sales of the Company’s capital stock (including redeemable convertible preferred stock), the effect of the rights and preferences of the preferred shareholders, and the prospects of a liquidity event, among others.

2014 Stock Incentive Plan – In March 2014, the Company’s board of directors adopted and its stockholders approved the 2014 Stock Incentive Plan, or the 2014 Plan, which became effective upon the closing of the IPO. The 2014 Plan provides for the grant of incentive stock options, nonstatutory stock options, stock appreciation rights, restricted stock, restricted stock units and other stock-based awards. The 2014 Plan provides an annual increase in the number of shares available for grant on the first day of each calendar year beginning with the fiscal year ended December 31, 2015 and continuing for each fiscal year until, and including, the fiscal year ending December 31, 2024, equal to the lesser of (i) 1,000,000 shares of common stock, (ii) 4% of the number of outstanding shares of common stock on such date and (iii) an amount determined by the Company’s board of directors. As of December 31, 2015, there were 540,950 shares available for future grant under the 2014 Plan.

A summary of stock option activity for employee and nonemployee awards under the 2007 Plan and the 2014 Plan during the year ended December 31, 2015 is presented below (Aggregate Intrinsic Value in thousands):

	Number of Shares			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Life (Years)		Aggregate Intrinsic Value
Outstanding — January 1, 2015		2,126,176		$	4.97		6.7	$	2,701
Granted		2,360,682			5.66
Exercised		(370,230	)		4.40
Forfeited		(661,702	)		5.86
Outstanding — December 31, 2015		3,454,926		$	5.39		8.9	$	—
Options expected to vest — December 31, 2015		2,336,878		$	5.32		9.4	$	—
Options exercisable — December 31, 2015		1,001,415		$	5.56		7.7	$	—

The total intrinsic value of stock options exercised in the years ended December 31, 2015, 2014, and 2013 was $0, $161,000, and $15,000, respectively.

The weighted-average per share grant date fair value of options granted during 2015, 2014, and 2013 was $3.22, $3.33, and $2.90, respectively.

The Company has recorded stock-based compensation expense of $2.4 million, $885,000, and $622,000 during the years ended December 31, 2015, 2014, and 2013, respectively, which is based on the number of awards ultimately expected to vest. As of December 31, 2015, there was $6.1 million of unrecognized compensation cost related to unvested stock-based compensation arrangements granted under the 2007 Plan and the 2014 Plan. The compensation is expected to be recognized over a weighted-average period of 2.88 years at December 31, 2015.

Stock-based compensation expense recorded as research and development and general and administrative expenses is as follows (in thousands):

	As of December 31,
	2015		2014		2013
Research and development	$	795	$	317	$	284
General and administrative		1,580		568		338
Total	$	2,375	$	885	$	622

The fair value of each option award is estimated on the date of grant using the Black-Scholes option-pricing model based on the assumptions noted in the table below. Expected volatility for the Company’s common stock was determined based on an average of the historical volatility of a peer-group of similar public companies. The Company has limited option exercise information, as such, the expected term of the options granted was calculated using the simplified method that represents the average of the contractual term of the option and the weighted-average vesting period of the option. The assumed dividend yield is based upon the Company’s expectation of not paying dividends in the foreseeable future. The risk-free rate for periods within the contractual life of the option is based upon the U.S. Treasury yield curve in effect at the time of grant.

The assumptions used in the Black-Scholes option-pricing model for stock options granted to employees during the years ended December 31, 2015, 2014, and 2013 are as follows:

	December 31,
	2015	2014	2013
Expected life	6 years	6 years	6 years
Risk-free interest rate	1.45%-2.02%	1.71%-2.00%	1.09%-1.92%
Expected volatility	51%-63%	54%-60%	59%-79%
Expected dividend rate	—%	—%	—%

The Company recorded stock-based compensation expense related to nonemployee awards of $173,000, $56,000, and $85,000 for the years ended December 31, 2015, 2014, and 2013, respectively. The compensation expense related to the nonemployee awards is included in the total stock-based compensation each year and is subject to re-measurement until the options vest. The Black-Scholes assumptions used to estimate the fair value of these awards for the years ended December 31, 2015, 2014, and 2013 were as follows:

	December 31,
	2015	2014	2013
Expected life	10 years	8 years	7 years
Risk-free interest rate	2.10%-2.25%	1.86%-2.53%	1.11%-2.86%
Expected volatility	60%-61%	56%-62%	56%-79%
Expected dividend rate	—%	—%	—%

During the year ended December 31, 2015, the Company granted nonemployee stock options to consultants for the purchase of 204,000 shares of the Company’s common stock. The weighted-average exercise price and the weighted-average fair value of nonemployee stock options granted for the year ended December 31, 2015, was $5.17 per share and $1.58 per share, respectively. The fair value of the grants is being expensed over the vesting period of the options on a straight-line basis as the services are being provided. On September 4, 2015, nonemployee stock options to purchase 90,000 shares of the Company’s common stock were converted to employee stock options upon the appointment of the Company’s Chief Medical Officer who had been serving as a consultant to the Company until his appointment. The exercise price and the fair value of these stock options is $4.71 per share and $2.71 per share, respectively. The Company did not grant any nonemployee stock option grants in 2014 or in 2013, except for a performance award grant in 2013 to the Company’s board chairman for non-board related services. During the year ended December 31, 2014, the board of directors changed the vesting conditions of this award from performance-based vesting to time-based vesting and reduced the total number of shares subject to the stock option. As a result, the 16,000 shares subject to this stock option now vest over three years, with the first third vesting on March 26, 2014. The change in vesting condition was accounted for as a modification of this stock option, which had an immaterial impact on the Company’s financial statements.

In 2012, the Company granted options to purchase 60,934 common shares to an officer of the Company, now the Company’s Chief Executive Officer, that will vest upon the achievement of business milestones as defined within the stock option agreement. These awards have not vested as of December 31, 2015. Compensation expense for the awards will be recorded if and when the awards are determined to be probable.

2014 Employee Stock Purchase Plan – In March 2014, the Company’s board of directors adopted and its stockholders approved the 2014 Employee Stock Purchase Plan (the “2014 ESPP”), which became effective upon the closing of the IPO. The 2014 ESPP will be administered by the Company’s board of directors or by a committee appointed by the Company’s board of directors. The 2014 ESPP initially provides participating employees with the opportunity to purchase up to an aggregate 500,000 of shares of the Company’s common stock. The number of shares of the Company’s common stock reserved for issuance under the 2014 ESPP will automatically increase on the first day of each fiscal year, commencing on January 1, 2015 and ending January 1, 2024, in an amount equal to the least of (i) 600,000 shares of the Company’s common stock, (ii) 1% of the total number of shares of the Company’s common stock outstanding on the first day of the applicable year, or (iii) an amount determined by the Company’s board of directors. There are two six-month offerings per year. The first offering period under the 2014 ESPP began on July 1, 2015. The compensation expense related to the 2014 ESPP is included in the total stock-based compensation. The stock-based compensation expense related to the ESPP for the year ended December 31, 2015, was $27,000. There was no stock-based compensation related to the 2014 ESPP recorded for the year ended December 31, 2014.

Fair Value Measurements

12 Months Ended

Dec. 31, 2015

Fair Value Disclosures [Abstract]

Fair Value Measurements

10.	FAIR VALUE MEASUREMENTS

The Company’s financial instruments consist of cash equivalents, accounts payable, accrued expenses, debt obligations, and preferred stock warrants. The carrying amount of accounts payable and accrued expenses are considered a reasonable estimate of their fair value, due to the short-term maturity of these instruments. The carrying amount of debt is also considered to be a reasonable estimate of the fair value based on the short-term nature of the debt and that the debt bears interest at the prevailing market rate for instruments with similar characteristics. If recorded at fair value, Level 2 measurements, as defined below, would have been used to estimate the fair value. Included in cash and cash equivalents as of December 31, 2015 and 2014, are money market fund investments of $75,325,000 and $50,541,000, respectively, which are reported at fair value.

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 are performed in a manner to maximize the use of observable inputs and minimize the use of unobservable inputs.

The accounting standard describes a fair value hierarchy based on three levels of inputs, of which the first two are considered observable and the last unobservable, that may be used to measure fair value, which are the following:

Level 1 — Quoted prices in active markets that are accessible at the market date for identical unrestricted assets or liabilities.

Level 2 — Inputs other than Level 1 that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs for which all significant inputs are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities.

Level 3 — Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities.

A summary of the financial assets and liabilities that are measured on a recurring basis at fair value as of December 31, 2015 and 2014, is as follows (in thousands):

			Fair Value Measurements Using
	Carrying		Quoted Prices in Active Markets for Identical Assets		Significant Other Observable Inputs		Significant Unobservable Inputs
	Value		(Level 1)		(Level 2)		(Level 3)
December 31, 2015
Money market funds	$	75,325	$	—	$	75,325	$	—
December 31, 2014
Money market funds	$	50,541	$	—	$	50,541	$	—

The Company’s money market funds have been valued on the basis of valuations provided by third-party pricing services, as derived from such services’ pricing models. Inputs to the models may include, but are not limited to, reported trades, executable bid and asked prices, broker/dealer quotations, prices or yields of securities with similar characteristics, benchmark curves or information pertaining to the issuer, as well as industry and economic events. The pricing services may use a matrix approach, which considers information regarding securities with similar characteristics to determine the valuation for a security. The Company is ultimately responsible for the consolidated financial statements and underlying estimates. Accordingly, the Company assesses the reasonableness of the valuations provided by the third-party pricing services by reviewing actual trade data, broker/dealer quotes and other similar data, which are obtained from quoted market prices or other sources.

For the years ended December 31, 2015 and 2014, there have been no transfers between levels.

The reconciliation of the Company’s liabilities measured at fair value on a recurring basis using unobservable inputs (Level 3) is as follows:

	Preferred Stock Warrant
	Series B			Series C			Series D			Total
Balance — December 31, 2013		4			386			538			928
Fair value reclassified to additional paid-in capital in connection with the completion of the IPO on April 15, 2014		(4	)		(386	)		(538	)		(928	)
Balance — December 31, 2014	$	—		$	—		$	—		$	—

The Company’s warrants were valued using the Black-Scholes option-pricing model. The fair values were derived by applying the following assumptions:

		December 31, 2013
Expected life		4-8 years
Risk-free interest rate		2.90%
Expected volatility		64%-84%
Expected dividend rate		—%

The preferred stock warrants were automatically adjusted on the date of the closing of the IPO to provide for the issuance of shares of common stock upon their exercise, and is no longer measured at fair value.

- 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

Income Taxes

12 Months Ended

Dec. 31, 2015

Income Tax Disclosure [Abstract]

Income Taxes

11.	INCOME TAXES

Significant components of the Company’s deferred taxes at December 31, 2014, and 2013 are as follows:

	2015			2014
Net operating loss carryforwards	$	35,797		$	29,442
Research and development credit carryforwards		2,066			1,715
Capitalized costs		3,977			3,503
Capitalized research and development costs		17,715			9,938
Other		903			422
Total deferred tax assets		60,458			45,020
Valuation allowance		(60,458	)		(45,020	)
Net deferred tax assets	$	—		$	—

The Company has provided a valuation allowance for the full amount of deferred tax assets as the realization of the deferred tax assets is not determined to be more-likely-than-not. The valuation allowance increased in 2015 and 2014 by approximately $15.6 million and $7.6 million, respectively, due to the increase in the deferred tax assets by the same amount. The increases are mainly attributable to operating losses generated in the period.

A reconciliation of income tax expense computed at the statutory federal income tax rate to income taxes as reflected in the financial statements is as follows:

	Years Ended December 31,
	2015			2014
Federal income tax expense at statutory rate		34.0	%		34.0	%
State income tax, net of federal benefit		5.0	%		4.5	%
Permanent differences		(0.5	%)		(3.7	%)
Research and development credit		0.9	%		0.8	%
Stock compensation		(0.7	%)		(0.9	%)
Expiration of state net operating loss		0.0	%		(1.7	%)
Other		0.4	%		(0.8	%)
Change in valuation allowance		(39.1	%)		(32.2	%)
Effective income tax rate		0.0	%		0.0	%

At December 31, 2015, the Company has approximately $93.7 million of federal and $74.1 million of state net operating loss carryforwards that expire at various dates through 2035. At December 31, 2015, the Company has approximately $1.4 million of federal and $0.9 million of state research and development credit carryforwards that expire at various dates through 2035 for federal credits and 2030 for state credits.

At December 31, 2014, the Company has approximately $77.3 million of federal and $58.1 million of state net operating loss carryforwards that expire at various dates through 2034. At December 31, 2014, the Company has approximately $1.2 million of federal and $0.8 million of state research and development credit carryforwards that expire at various dates through 2034 for federal credits and 2029 for state credits.

Realization of the future tax benefits is dependent on many factors, including the Company’s ability to generate taxable income within the net operating loss carryforward period. The future realization of the net operating loss carryforwards may also be limited by the change of ownership rules of the Internal Revenue Service under Section 382 of the Internal Revenue Code. If substantial changes in ownership should occur, there could be annual limitations on the amount of carryforwards that can be realized in future periods.

The Company files income tax returns in the United States, the Commonwealth of Massachusetts, and Australia. The tax years 2006 through 2014 remain open to examination by these taxing jurisdictions, as carryforwards attributes generated in past years may be adjusted in a future period. The Company is currently not under examination by the Internal Revenue Service or any other jurisdictions for any tax years. At December 31, 2015 and 2014, the Company has not identified any significant uncertain tax positions.

Commitments

12 Months Ended

Dec. 31, 2015

Commitments And Contingencies Disclosure [Abstract]

Commitments

12.	COMMITMENTS

Facility Lease — On November 1, 2009, the Company entered into a noncancelable operating lease with a third party for office and laboratory space that was scheduled to expire in February 2013, subject to a three-year renewal option. In June 2012, the Company exercised its renewal option extending the lease through February 2016. On July 11, 2014, the Company signed a lease amendment for additional office space in the same building to expire concurrent with the lease agreement in February 2016. The Company terminated the lease agreement early in December 2015 without penalty. The lease agreement and amendment included base rent escalation over the lease term therefore, the Company amortized the cost of the lease on a straight-line basis over the lease term. The resulting deferred liability recorded in other current and long-term liabilities as of December 31, 2014 was $41,000. Rent expense under this lease was $920,000, $766,000, and $598,000 for the years ended December 31, 2015, 2014, and 2013, respectively.

On July 9, 2015, the Company entered into a noncancelable operating lease with a third party for office, laboratory and vivarium space that is scheduled to expire in February 2021, subject to a three-year renewal option. The lease agreement includes base rent escalation over the lease term which will be amortized on a straight-line basis over the lease term with the resulting deferred liability recorded in other current and long-term liabilities. The lease requires the Company to share in prorated expenses and property taxes based upon actual amounts incurred; those amounts are not fixed for future periods and, therefore, not included in the future minimum obligations listed below.

Future minimum lease payments under the non-cancelable operating lease are as follows (in thousands):

	Operating
Years Ending December 31,	Leases
2016	$	575
2017		690
2018		738
2019		786
2020		830
2021		140
Total	$	3,759

Licensing Agreements

12 Months Ended

Dec. 31, 2015

Research And Development Expense [Abstract]

Licensing Agreements

13.	LICENSING AGREEMENTS

Calando License — The Company has a product license agreement and a platform license agreement with Calando Pharmaceuticals, Inc. (“Calando”). Under the product license agreement, the Company may be required to pay Calando up to $32.8 million upon the achievement of specified regulatory and commercial milestones and pay tiered royalty payment ranging from low-to mid-single digits on commercial sales.

Under the platform license agreement, the Company paid Calando a $250,000 clinical development milestone which was recorded in December 2014 upon initiation of the Phase 1/2a clinical trial for CRLX301. The Company may be required to make additional milestone payments to Calando of up to $17.8 million, in the aggregate, upon the achievement of specified regulatory and commercial milestones and pay royalty payments ranging from low-to mid-single digits on commercial sales.

In March 2014, Calando entered Chapter 7 bankruptcy in the District of Delaware and, as a result, the intellectual property rights the Company has obtained from Calando are subject to potential risks that may arise in connection with bankruptcy. For instance, while the Company’s ability to develop and/or commercialize its current product candidates and its ability to utilize its platform are not dependent on the rights that it licenses from Calando, its license agreements with Calando could be rejected in connection with Calando’s bankruptcy, in which case, the Company could, subject to elections and other rights and defenses that may be available to it, lose certain rights granted to it under such licenses. On March 3, 2015, Calando’s bankruptcy trustee submitted an application with the bankruptcy court seeking authority to retain a broker to sell Calando’s rights in certain assets including its rights in the license agreements with the Company, the Company has reserved its rights with respect to any such sale.

SUNY License — The Company is party to a license agreement with The Research Foundation of State University of New York (“SUNY”) for certain intellectual property. The agreement as amended requires the Company to pay nonrefundable annual license maintenance fees each year until the date of first commercial sale of a licensed product pursuant to the license agreement, as amended. The annual license fee is not material in any individual year. In the event of future partner collaborations or product sales incorporating technology covered by this license agreement, the Company may be required to pay milestone payments and/or product royalties. In connection with this agreement, the Company recorded research and development expense of $36,000, $30,000, and $25,000 for the years ended December 31, 2015, 2014, and 2013, respectively.

Massachusetts Institute of Technology License — The Company delivered a notice of termination which became effective on November 1, 2015, with respect to the Company’s license agreement with the Massachusetts Institute of Technology (“MIT”). The agreement as amended required the Company to pay MIT nonrefundable annual license maintenance fees that increased each year beginning in 2015. In connection with this agreement, the Company recorded research and development expense for annual maintenance fees of $50,000 for the year ended December 31, 2015, and $10,000 each in the years ended December 31, 2014 and 2013.

Retirement Plans

12 Months Ended

Dec. 31, 2015

Compensation And Retirement Disclosure [Abstract]

Retirement Plans

14.	RETIREMENT PLANS

The Company has a 401(k) retirement and profit-sharing plan (the “401(k) Plan”) covering all qualified employees. The 401(k) Plan allows each participant to contribute a portion of their base wages up to an amount not to exceed an annual statutory maximum. Effective January 1, 2010, the Company adopted a Safe Harbor Plan that provides a Company match up to 4% of salary. The Company contributed a match of $264,000, $163,000, and $145,000 to the 401(k) Plan for the years ended December 31, 2015, 2014, and 2013, respectively.

Related Party Transactions

12 Months Ended

Dec. 31, 2015

Related Party Transactions

15.	RELATED PARTY TRANSACTIONS

In April 2013, the Company entered into a laboratory, equipment sharing, services and license agreement with an entity affiliated with one of the Company’s directors. Fees recorded offsetting research and development expenses under this agreement and paid in the year ended December 31, 2014 and 2013, were $39,000 and $84,000, respectively. On April 1, 2014, the Company sold used equipment to this entity and recorded proceeds from the sale of $30,000. The agreement was terminated on April 1, 2014.

In August 2013 and February 2014, the Company issued convertible promissory notes to existing investors, as described in Note 6. In April 2014, these notes were converted into the Company’s common stock in connection with the IPO.

In April 2014, the Company converted all outstanding shares of the Company’s preferred stock held by existing investors into 6,826,004 shares of the Company’s common stock in connection with the IPO.

- 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

Revenue

12 Months Ended

Dec. 31, 2015

Revenues [Abstract]

Revenue

16.

REVENUE

In October 2013, the Company entered into a material transfer agreement with biopharmaceutical company to conduct feasibility studies using the Company’s proprietary technology. The Company recognized revenue of $61,000 and $6,000 for the years ended December 31, 2014 and 2013, respectively, in connection with this material transfer agreement. The Company had no revenue for the year ended December 31, 2015.

In May 2013, the Company entered into a material transfer agreement with another biopharmaceutical company to conduct feasibility studies using the Company’s proprietary technology. The Company recognized revenue of $19,000 for the year ended December 31, 2014, in connection with this material transfer agreement.

Quarterly Financial Data (Unaudited)

12 Months Ended

Dec. 31, 2015

Quarterly Financial Information Disclosure [Abstract]

Quarterly Financial Data (Unaudited)

17.	QUARTERLY FINANCIAL DATA (unaudited)

The following table summarizes the unaudited quarterly financial data for the last two fiscal years:

CONSOLIDATED STATEMENTS OF OPERATIONS (in thousands, except share data and per share data)

	Year Ended December 31, 2015
	First Quarter			Second Quarter			Third Quarter			Fourth Quarter
Revenue	$	—		$	—		$	—		$	—
Operating expenses:
Research and development		5,021			6,678			7,092			7,157
General and administrative		2,681			2,717			2,954			2,872
Total operating expenses		7,702			9,395			10,046			10,029
Other income (expense):
Interest income		3			1			4			2
Interest expense		(721	)		(513	)		(509	)		(689	)
Total other income (expense) — net		(718	)		(512	)		(505	)		(687	)
Net loss attributable to common stockholders	$	(8,420	)	$	(9,907	)	$	(10,551	)	$	(10,716	)
Net loss per share attributable to common stockholders:
Basic and diluted	$	(0.41	)	$	(0.37	)	$	(0.39	)	$	(0.39	)
Weighted-average common shares outstanding:
Basic and diluted		20,350,557			26,690,673			27,307,103			27,346,780

	Year Ended December 31, 2014
	First Quarter			Second Quarter			Third Quarter			Fourth Quarter
Revenue	$	47		$	33		$	—		$	—
Operating expenses:
Research and development		1,495			2,648			2,928			4,701
General and administrative		1,510			2,029			2,441			2,607
Total operating expenses		3,005			4,677			5,369			7,308
Other income (expense):
Interest income		1			2			2			4
Interest expense		(461	)		(268	)		(191	)		(163	)
Loss on extinguishment of debt		—			(2,493	)		—			—
Decrease in value of preferred stock warrant liability		504			—			—			—
Total other income (expense) — net		44			(2,759	)		(189	)		(159	)
Net loss attributable to common stockholders	$	(2,914	)	$	(7,403	)	$	(5,558	)	$	(7,467	)
Net loss per share attributable to common stockholders:
Basic and diluted	$	(3.70	)	$	(0.44	)	$	(0.28	)	$	(0.37	)
Weighted-average common shares outstanding:
Basic and diluted		786,986			16,883,716			20,124,574			20,125,009

Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2015

Accounting Policies [Abstract]

Use of Estimates

Principles of Consolidation

Segment Information

Cash and Cash Equivalents

Cash and Cash Equivalents — Cash equivalents include all highly liquid investments maturing within 90 days from the date of purchase and consist primarily of money market funds.

Concentrations of Credit Risk

Restricted Cash

Property and Equipment

Depreciation is provided using the straight-line method over the following estimated useful lives:

Laboratory equipment		5 years
Computer equipment		3 years
Office furniture and equipment		5 years
Leasehold improvements		Lesser of useful life or remaining lease term

Impairment of Long-Lived Assets

Revenue Recognition

Comprehensive Loss

Research and Development Costs

Preferred Stock Warrant Liability

Redeemable Convertible Preferred Stock

Stock-Based Compensation

Net Loss per Share Attributable to Common Stockholders

Income Taxes

Guarantees and Indemnification

Recent Accounting Pronouncements

Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2015

Accounting Policies [Abstract]

Schedule of Property and Equipment Estimated Useful Lives

Depreciation is provided using the straight-line method over the following estimated useful lives:

Laboratory equipment		5 years
Computer equipment		3 years
Office furniture and equipment		5 years
Leasehold improvements		Lesser of useful life or remaining lease term

Net Loss Per Share Attributable to Common Stockholders (Tables)

12 Months Ended

Dec. 31, 2015

Earnings Per Share [Abstract]

Schedule of Basic and Diluted Net Loss Per Common Share

The following table summarizes the computation of basic and diluted net loss per share attributable to common stockholders of the Company (in thousands, except share data and per share data):

	Years Ended December 31,
	2015			2014			2013
Net loss attributable to common stockholders — basic and diluted	$	(39,594	)	$	(23,342	)	$	(17,143	)
Weighted-average number of common shares — basic and diluted		25,431,332			14,548,516			684,330
Net loss per share attributable to common stockholders — basic and diluted	$	(1.56	)	$	(1.60	)	$	(25.05	)

Potentially Dilutive Securities Excluded from Computation of Diluted Weighted-Average Shares Outstanding

	As of December 31,
	2015		2014		2013
Options to purchase common stock		3,454,926		2,126,176		1,062,694
Warrants to purchase redeemable convertible preferred stock		—		—		128,663
Warrants to purchase common stock		300,564		128,663		—
Redeemable convertible preferred stock		—		—		6,826,004
Convertible notes payable		—		—		754,785

Property and Equipment (Tables)

12 Months Ended

Dec. 31, 2015

Property Plant And Equipment [Abstract]

Summary of Property and Equipment

Property and equipment consist of the following (in thousands):

	As of December 31,
	2015			2014
Laboratory equipment	$	1,314		$	1,163
Computer equipment		350			260
Office furniture and equipment		25			292
Leasehold improvements		33			117
		1,722			1,832
Less accumulated depreciation and amortization		(1,146	)		(1,490	)
Property and equipment, net	$	576		$	342

Accrued Expenses (Tables)

12 Months Ended

Dec. 31, 2015

Payables And Accruals [Abstract]

Schedule of Accrued Expenses

Accrued expenses consist of the following (in thousands):

	As of December 31,
	2015		2014
Accrued clinical trial costs	$	2,631	$	848
Accrued contract manufacturing expenses		945		580
Accrued compensation and benefits		1,864		983
Accrued interest		136		574
Other accrued expenses		883		663
Total accrued expenses	$	6,459	$	3,648

Loan Agreements (Tables)

12 Months Ended

Dec. 31, 2015

Debt Instrument [Line Items]

Summary of Minimum Future Principal Payments

The minimum future principal payments are as follows (in thousands):

Year Ending December 31,
2016	$	7,945
2017		8,544
2018		4,511
Unamortized discount relating to warrants and deferred financing costs		(676	)
Total		20,324
Less current portion		(7,652	)
Long-term portion	$	12,672

Fair Value of Stock Warrants Calculated using Black-Scholes Assumptions

The Company’s warrants were valued using the Black-Scholes option-pricing model. The fair values were derived by applying the following assumptions:

		December 31, 2013
Expected life		4-8 years
Risk-free interest rate		2.90%
Expected volatility		64%-84%
Expected dividend rate		—%

Hercules Loan Agreement [Member] | Common Stock Warrants [Member]

Debt Instrument [Line Items]

Fair Value of Stock Warrants Calculated using Black-Scholes Assumptions

The following table shows the Black-Scholes assumptions used to value the warrant:

	January 8, 2015
Contractual life	5 years
Volatility rate		61	%
Risk-free interest rate		1.5	%
Expected dividends		—

Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2015

Stockholders Equity Note [Abstract]

Summary of Number of Shares of Common Stock Reserved

The Company has reserved the following number of shares of common stock at December 31, 2015 and 2014:

	As of December 31,
	2015		2014
Warrants to purchase common stock		300,564		128,663
Common stock options		3,995,876		3,561,104
Total		4,296,440		3,689,767

Stock Option Plans (Tables)

12 Months Ended

Dec. 31, 2015

Summary of Stock Option Activity for Employee and Nonemployee Awards under Plan

	Number of Shares			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Life (Years)		Aggregate Intrinsic Value
Outstanding — January 1, 2015		2,126,176		$	4.97		6.7	$	2,701
Granted		2,360,682			5.66
Exercised		(370,230	)		4.40
Forfeited		(661,702	)		5.86
Outstanding — December 31, 2015		3,454,926		$	5.39		8.9	$	—
Options expected to vest — December 31, 2015		2,336,878		$	5.32		9.4	$	—
Options exercisable — December 31, 2015		1,001,415		$	5.56		7.7	$	—

Schedule of Stock-based Compensation Expense

Stock-based compensation expense recorded as research and development and general and administrative expenses is as follows (in thousands):

	As of December 31,
	2015		2014		2013
Research and development	$	795	$	317	$	284
General and administrative		1,580		568		338
Total	$	2,375	$	885	$	622

Summary of Assumptions Used in Black-Scholes Option-Pricing Model for Stock Options Granted to Employees and Non Employees

The assumptions used in the Black-Scholes option-pricing model for stock options granted to employees during the years ended December 31, 2015, 2014, and 2013 are as follows:

	December 31,
	2015	2014	2013
Expected life	6 years	6 years	6 years
Risk-free interest rate	1.45%-2.02%	1.71%-2.00%	1.09%-1.92%
Expected volatility	51%-63%	54%-60%	59%-79%
Expected dividend rate	—%	—%	—%

Non Employee Awards [Member]

Summary of Assumptions Used in Black-Scholes Option-Pricing Model for Stock Options Granted to Employees and Non Employees

The Black-Scholes assumptions used to estimate the fair value of these awards for the years ended December 31, 2015, 2014, and 2013 were as follows:

	December 31,
	2015	2014	2013
Expected life	10 years	8 years	7 years
Risk-free interest rate	2.10%-2.25%	1.86%-2.53%	1.11%-2.86%
Expected volatility	60%-61%	56%-62%	56%-79%
Expected dividend rate	—%	—%	—%

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2015

Fair Value Disclosures [Abstract]

Summary of Financial Assets and Liabilities Measured on Recurring Basis at Fair Value

A summary of the financial assets and liabilities that are measured on a recurring basis at fair value as of December 31, 2015 and 2014, is as follows (in thousands):

			Fair Value Measurements Using
	Carrying		Quoted Prices in Active Markets for Identical Assets		Significant Other Observable Inputs		Significant Unobservable Inputs
	Value		(Level 1)		(Level 2)		(Level 3)
December 31, 2015
Money market funds	$	75,325	$	—	$	75,325	$	—
December 31, 2014
Money market funds	$	50,541	$	—	$	50,541	$	—

Reconciliation of Company's Liabilities Measured at Fair Value on Recurring Basis Using Unobservable Inputs (Level 3)

The reconciliation of the Company’s liabilities measured at fair value on a recurring basis using unobservable inputs (Level 3) is as follows:

	Preferred Stock Warrant
	Series B			Series C			Series D			Total
Balance — December 31, 2013		4			386			538			928
Fair value reclassified to additional paid-in capital in connection with the completion of the IPO on April 15, 2014		(4	)		(386	)		(538	)		(928	)
Balance — December 31, 2014	$	—		$	—		$	—		$	—

Fair Value of Stock Warrants Calculated using Black-Scholes Assumptions

The Company’s warrants were valued using the Black-Scholes option-pricing model. The fair values were derived by applying the following assumptions:

		December 31, 2013
Expected life		4-8 years
Risk-free interest rate		2.90%
Expected volatility		64%-84%
Expected dividend rate		—%

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2015

Income Tax Disclosure [Abstract]

Significant Components of Company's Deferred Taxes

Significant components of the Company’s deferred taxes at December 31, 2014, and 2013 are as follows:

	2015			2014
Net operating loss carryforwards	$	35,797		$	29,442
Research and development credit carryforwards		2,066			1,715
Capitalized costs		3,977			3,503
Capitalized research and development costs		17,715			9,938
Other		903			422
Total deferred tax assets		60,458			45,020
Valuation allowance		(60,458	)		(45,020	)
Net deferred tax assets	$	—		$	—

Reconciliation of Income Tax Expense Computed at Statutory Federal Income Tax Rate to Income Taxes

A reconciliation of income tax expense computed at the statutory federal income tax rate to income taxes as reflected in the financial statements is as follows:

	Years Ended December 31,
	2015			2014
Federal income tax expense at statutory rate		34.0	%		34.0	%
State income tax, net of federal benefit		5.0	%		4.5	%
Permanent differences		(0.5	%)		(3.7	%)
Research and development credit		0.9	%		0.8	%
Stock compensation		(0.7	%)		(0.9	%)
Expiration of state net operating loss		0.0	%		(1.7	%)
Other		0.4	%		(0.8	%)
Change in valuation allowance		(39.1	%)		(32.2	%)
Effective income tax rate		0.0	%		0.0	%

Commitments (Tables)

12 Months Ended

Dec. 31, 2015

Commitments And Contingencies Disclosure [Abstract]

Summary of Future Minimum Lease Payments under Non-cancelable Operating Leases

Future minimum lease payments under the non-cancelable operating lease are as follows (in thousands):

	Operating
Years Ending December 31,	Leases
2016	$	575
2017		690
2018		738
2019		786
2020		830
2021		140
Total	$	3,759

Quarterly Financial Data (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2015

Quarterly Financial Information Disclosure [Abstract]

Schedule of Quarterly Financial Data

The following table summarizes the unaudited quarterly financial data for the last two fiscal years:

CONSOLIDATED STATEMENTS OF OPERATIONS (in thousands, except share data and per share data)

	Year Ended December 31, 2015
	First Quarter			Second Quarter			Third Quarter			Fourth Quarter
Revenue	$	—		$	—		$	—		$	—
Operating expenses:
Research and development		5,021			6,678			7,092			7,157
General and administrative		2,681			2,717			2,954			2,872
Total operating expenses		7,702			9,395			10,046			10,029
Other income (expense):
Interest income		3			1			4			2
Interest expense		(721	)		(513	)		(509	)		(689	)
Total other income (expense) — net		(718	)		(512	)		(505	)		(687	)
Net loss attributable to common stockholders	$	(8,420	)	$	(9,907	)	$	(10,551	)	$	(10,716	)
Net loss per share attributable to common stockholders:
Basic and diluted	$	(0.41	)	$	(0.37	)	$	(0.39	)	$	(0.39	)
Weighted-average common shares outstanding:
Basic and diluted		20,350,557			26,690,673			27,307,103			27,346,780

	Year Ended December 31, 2014
	First Quarter			Second Quarter			Third Quarter			Fourth Quarter
Revenue	$	47		$	33		$	—		$	—
Operating expenses:
Research and development		1,495			2,648			2,928			4,701
General and administrative		1,510			2,029			2,441			2,607
Total operating expenses		3,005			4,677			5,369			7,308
Other income (expense):
Interest income		1			2			2			4
Interest expense		(461	)		(268	)		(191	)		(163	)
Loss on extinguishment of debt		—			(2,493	)		—			—
Decrease in value of preferred stock warrant liability		504			—			—			—
Total other income (expense) — net		44			(2,759	)		(189	)		(159	)
Net loss attributable to common stockholders	$	(2,914	)	$	(7,403	)	$	(5,558	)	$	(7,467	)
Net loss per share attributable to common stockholders:
Basic and diluted	$	(3.70	)	$	(0.44	)	$	(0.28	)	$	(0.37	)
Weighted-average common shares outstanding:
Basic and diluted		786,986			16,883,716			20,124,574			20,125,009

Nature of Business and Operations - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands				12 Months Ended
	Apr. 10, 2015	May 07, 2014	Apr. 15, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Nature Of Business And Operations [Line Items]
Date of Company's incorporation				Nov. 28, 2005
Accumulated deficit				$ 161,375	$ 121,781
Proceeds from sale of common stock				$ 2,628	$ 140	$ 35
Common Stock [Member]
Nature Of Business And Operations [Line Items]
Issuance and sale of common stock, Shares	6,716,000
Follow-on Offering [Member]
Nature Of Business And Operations [Line Items]
Common stock issuance date				Apr. 10, 2015
Issuance and sale of common stock, Shares	6,716,000
Common share offering price, per share	$ 6.00
Proceeds from sale of common stock	$ 37,200
Follow-on Offering [Member] \| Common Stock [Member]
Nature Of Business And Operations [Line Items]
Issuance and sale of common stock, Shares				6,716,000
Option Exercised by Underwriter [Member]
Nature Of Business And Operations [Line Items]
Issuance and sale of common stock, Shares	876,000
IPO [Member]
Nature Of Business And Operations [Line Items]
Common stock issuance date					Apr. 15, 2014
Issuance and sale of common stock, Shares		1,069,715	8,500,000
Issuance/sale of stock, price per share		$ 7.00	$ 7.00
Proceeds from initial public offering, net		$ 59,900
Preferred stock conversion basis				In connection with the closing of the IPO, all of the Company's outstanding redeemable convertible preferred stock and convertible notes automatically converted into shares of common stock as of April 15, 2014
IPO [Member] \| Preferred Stock Warrants [Member]
Nature Of Business And Operations [Line Items]
Warrant to purchase stock, number of securities called by warrants or rights			1,857,226
IPO [Member] \| Common Stock Warrants [Member]
Nature Of Business And Operations [Line Items]
Number of automatically converted shares			128,663
IPO [Member] \| Common Stock [Member]
Nature Of Business And Operations [Line Items]
Issuance and sale of common stock, Shares					9,569,715
Number of automatically converted shares			9,728,237

Significant Accounting Policies - Additional Information (Detail)	3 Months Ended		12 Months Ended
	Jun. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	Dec. 31, 2015 USD ($) Segment	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Significant Accounting Policies [Line Items]
Number of operating segments \| Segment			1
Revenue	$ 33,000	$ 47,000		$ 80,000	$ 6,000
Restricted cash			$ 347,000	$ 117,000
Facility lease scheduled expiration period			2016-02
Unamortized deferred financing costs			$ 200,000
New Facility Lease [Member]
Significant Accounting Policies [Line Items]
Facility lease scheduled expiration period			2021-02
Sydney, NSW [Member]
Significant Accounting Policies [Line Items]
Revenue			$ 0
Long-lived assets			$ 0

Significant Accounting Policies - Schedule of Property and Equipment Estimated Useful Lives (Detail)	12 Months Ended
	Dec. 31, 2015
Laboratory Equipment [Member]
Property Plant And Equipment [Line Items]
Property and equipment estimated useful life	5 years
Computer Equipment [Member]
Property Plant And Equipment [Line Items]
Property and equipment estimated useful life	3 years
Office Furniture and Equipment [Member]
Property Plant And Equipment [Line Items]
Property and equipment estimated useful life	5 years
Leasehold Improvements [Member]
Property Plant And Equipment [Line Items]
Property and equipment estimated useful life	Lesser of useful life or remaining lease term

Net Loss Per Share Attributable to Common Stockholders - Schedule of Basic and Diluted Net Loss Per Common Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Earnings Per Share [Abstract]
Net loss attributable to common stockholders									$ (39,594)	$ (23,342)	$ (17,143)
Weighted-average number of common shares — basic and diluted	27,346,780	27,307,103	26,690,673	20,350,557	20,125,009	20,124,574	16,883,716	786,986	25,431,332	14,548,516	684,330
Net loss per share attributable to common stockholders — basic and diluted	$ (0.39)	$ (0.39)	$ (0.37)	$ (0.41)	$ (0.37)	$ (0.28)	$ (0.44)	$ (3.70)	$ (1.56)	$ (1.60)	$ (25.05)

Net Loss Per Share Attributable to Common Stockholders - Potentially Dilutive Securities Excluded from Computation of Diluted Weighted-Average Shares Outstanding (Detail) - shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Redeemable Convertible Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted weighted-average shares outstanding			6,826,004
Options to Purchase Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted weighted-average shares outstanding	3,454,926	2,126,176	1,062,694
Warrants [Member] \| Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted weighted-average shares outstanding	300,564	128,663
Warrants [Member] \| Redeemable Convertible Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted weighted-average shares outstanding			128,663
Convertible Debt Securities
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted weighted-average shares outstanding			754,785

Property and Equipment - Summary of Property and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 1,722	$ 1,832
Less accumulated depreciation and amortization	(1,146)	(1,490)
Property and equipment, net	576	342
Laboratory Equipment [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	1,314	1,163
Computer Equipment [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	350	260
Office Furniture and Equipment [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	25	292
Leasehold Improvements [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 33	$ 117

Property and Equipment - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Property Plant And Equipment [Abstract]
Depreciation and amortization	$ 192	$ 126	$ 197

Accrued Expenses - Schedule of Accrued Expenses (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Payables And Accruals [Abstract]
Accrued clinical trial costs	$ 2,631	$ 848
Accrued contract manufacturing expenses	945	580
Accrued compensation and benefits	1,864	983
Accrued interest	136	574
Other accrued expenses	883	663
Total accrued expenses	$ 6,459	$ 3,648

Convertible Notes Payable to Shareholders - Additional Information (Detail)		1 Months Ended	2 Months Ended	3 Months Ended	12 Months Ended
	Nov. 30, 2010 USD ($) $ / shares shares	Apr. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	Jun. 30, 2014 USD ($)	Dec. 31, 2015	Dec. 31, 2014 USD ($)	Apr. 15, 2014 shares	Aug. 31, 2013 USD ($)	Sep. 30, 2010 USD ($)	May 31, 2010 USD ($)
Debt Instrument [Line Items]
Debt instrument, Original principal amount								$ 8,824,000
Debt instrument stated interest rate								7.00%
Debt instrument conversion of principal and accrued interest						$ 20,129,000
Loss on extinguishment of debt				$ (2,493,000)		$ (2,493,000)
Convertible Notes Payable [Member]
Debt Instrument [Line Items]
Debt instrument, Original principal amount									$ 1,500,000	$ 5,000,000
Debt instrument stated interest rate			7.00%						7.00%	7.00%
Preferred stock shares became exercisable \| shares							60,532
Fair value of warrants	$ 474,000
Expected volatility	80.00%
Expected life	7 years
Risk-free interest rate	1.85%
Dividend yield \| $ / shares	$ 0
Debt instrument, Conversion Ratio			0.775
IPO closure date					Apr. 15, 2014
Loss on extinguishment of debt		$ (2,493,000)
Convertible Notes Payable [Member] \| Existing Investors [Member]
Debt Instrument [Line Items]
Debt instrument, Original principal amount			$ 6,000,000
Convertible Notes Payable [Member] \| New Investor [Member]
Debt Instrument [Line Items]
Debt instrument, Original principal amount			$ 2,500,000
Convertible Notes Payable [Member] \| Series C Convertible Preferred Stock [Member]
Debt Instrument [Line Items]
Debt instrument conversion of principal and accrued interest	$ 176,000
Debt instrument conversion shares \| shares	9,021,175
Debt instrument conversion price \| $ / shares	$ 0.74
Percentage to determine the number of shares included in warrants	10.00%
Preferred stock shares became exercisable \| shares	878,370
Preferred stock per share \| $ / shares	$ 0.74

Loan Agreements - Additional Information (Detail)			1 Months Ended				6 Months Ended	12 Months Ended
Loan Agreements - Additional Information (Detail)	Apr. 10, 2015 shares	Jan. 08, 2015 USD ($) Tranches $ / shares shares	Jan. 31, 2015 USD ($)	Aug. 31, 2012 USD ($)	Mar. 31, 2012 USD ($)	Dec. 31, 2011 USD ($) $ / shares shares	Aug. 31, 2012 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 15, 2015 USD ($)	Nov. 24, 2015 USD ($)	Apr. 30, 2014 shares	Aug. 31, 2013
Debt Instrument [Line Items]
Principal outstanding under the Term Loan								$ 20,324,000
Proceeds from sale of common stock								2,628,000	$ 140,000	$ 35,000
Unamortized deferred financing costs								200,000
Unamortized discount on debt, relating to warrants								500,000
Proceeds from loan payable								21,000,000
Debt instrument stated interest rate														7.00%
Accrued interest								$ 136,000	574,000
Common Stock [Member]
Debt Instrument [Line Items]
Issuance of Common Stock, shares \| shares	6,716,000
Hercules Loan Agreement [Member] \| Term Loan [Member]
Debt Instrument [Line Items]
Prior written notice period to prepay term loan								7 days
Loan and Security Agreement with Lighthouse Capital [Member]
Debt Instrument [Line Items]
Accrued interest									$ 574,000
Loan and Security Agreement with Lighthouse Capital [Member] \| Loans payable [Member]
Debt Instrument [Line Items]
Loan and security agreement, maximum borrowing capacity						$ 10,000,000
Unamortized discount on debt, relating to warrants			$ 200,000
Proceeds from loan payable				$ 5,000,000	$ 5,000,000		$ 10,000,000
Loan and security agreement, borrowings repayment period						36 months
Debt instrument stated interest rate						8.25%
Loan and security agreement, borrowings repayment start date						Dec. 01, 2012
Line of credit facility, additional interest payment								$ 600,000
Repayments of notes payable			3,600,000
Loan and Security Agreement with Lighthouse Capital [Member] \| Loans payable [Member] \| Series D Convertible Preferred Stock [Member]
Debt Instrument [Line Items]
Exercise price of warrant \| $ / shares						$ 12.04
Warrant expiration date						2021-12
Warrant expiration period						10 years
Loan and Security Agreement with Lighthouse Capital [Member] \| Loans payable [Member] \| Common Stock [Member]
Debt Instrument [Line Items]
Warrant to purchase stock, number of securities called by warrants or rights \| shares													66,436
Loan and Security Agreement with Lighthouse Capital [Member] \| Maximum [Member] \| Loans payable [Member] \| Series D Convertible Preferred Stock [Member]
Debt Instrument [Line Items]
Warrant to purchase stock, number of securities called by warrants or rights \| shares						66,436
Hercules Technology Growth Capital, Inc. [Member] \| Hercules Loan Agreement [Member] \| Stock Purchase Agreement [Member]
Debt Instrument [Line Items]
Issuance of Common Stock, shares \| shares		135,501
Issuance/sale of stock, price per share \| $ / shares		$ 7.38
Proceeds from sale of common stock		$ 1,000,000
Hercules Technology Growth Capital, Inc. [Member] \| Hercules Loan Agreement [Member] \| Term Loan [Member]
Debt Instrument [Line Items]
Loan and security agreement, maximum borrowing capacity		$ 26,000,000
Principal outstanding under the Term Loan								$ 21,000,000
Term loan facility, maturity date		Jul. 01, 2018
Term loan facility, interest rate terms								The Term Loan will mature on July 1, 2018. Each advance under the Term Loan accrues interest at a floating per annum rate equal to the greater of (i) 7.30% or (ii) the sum of 7.30% plus the prime rate minus 5.75%. The Term Loan provided for interest-only payments on a monthly basis until December 31, 2015.
Additional interest rate during an event of default		5.00%
Term loan facility, interest rate		7.30%
Debt prepayment charge, after twelve months		2.00%
Debt prepayment charge, after twenty-four months		1.00%
Final payment as percentage of aggregate original principal amount		6.70%
Class of warrant or right, date until which warrants exercisable		Jan. 08, 2020
Estimated fair value of warrant			$ 824,000
Hercules Technology Growth Capital, Inc. [Member] \| Hercules Loan Agreement [Member] \| Term Loan [Member] \| Common Stock [Member]
Debt Instrument [Line Items]
Exercise price of warrant \| $ / shares		$ 6.05
Warrant to purchase stock, number of securities called by warrants or rights \| shares		171,901
Hercules Technology Growth Capital, Inc. [Member] \| Hercules Loan Agreement [Member] \| Term Loan [Member] \| Prime Rate [Member]
Debt Instrument [Line Items]
Term loan facility, interest rate spread		5.75%
Hercules Technology Growth Capital, Inc. [Member] \| Hercules Loan Agreement [Member] \| Term Loan [Member] \| Borrowing One [Member]
Debt Instrument [Line Items]
Loan and security agreement, maximum borrowing capacity		$ 15,000,000
Hercules Technology Growth Capital, Inc. [Member] \| Hercules Loan Agreement [Member] \| Term Loan [Member] \| Second Tranche [Member]
Debt Instrument [Line Items]
Loan and security agreement, maximum borrowing capacity												$ 6,000,000
Hercules Technology Growth Capital, Inc. [Member] \| Hercules Loan Agreement [Member] \| Term Loan [Member] \| Up on Meeting Certain Clinical Milestone on or Prior to Dec. 15, 2015 [Member]
Debt Instrument [Line Items]
Loan and security agreement, maximum borrowing capacity											$ 5,000,000
Hercules Technology Growth Capital, Inc. [Member] \| Hercules Loan Agreement [Member] \| Term Loan [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Number of tranches \| Tranches		3

Loan Agreements - Summary of Minimum Future Principal Payments (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Debt Disclosure [Abstract]
2016	$ 7,945
2017	8,544
2018	4,511
Unamortized discount relating to warrants and deferred financing costs	(676)
Total	20,324
Less current portion	(7,652)	$ (3,124)
Long-term portion	$ 12,672

Loan Agreements - Fair Value of Preferred Stock Warrants Calculated using Black-Scholes Assumptions (Detail) - Hercules Technology Growth Capital, Inc. [Member] - Hercules Loan Agreement [Member]	Jan. 08, 2015
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Contractual life	5 years
Volatility rate	61.00%
Risk-free interest rate	1.50%

Stockholders' Equity - Additional Information (Detail) - Common Stock [Member] - shares		12 Months Ended
	Apr. 10, 2015	Dec. 31, 2014
Class Of Stock [Line Items]
Issuance of common stock in underwritten public offering, shares	6,716,000
Issuance of common stock, shares		19,297,952

Stockholders' Equity - Summary of Number of Shares of Common Stock Reserved (Detail) - shares	Dec. 31, 2015	Dec. 31, 2014
Class Of Stock [Line Items]
Reserved shares of common stock	4,296,440	3,689,767
Common stock options [Member]
Class Of Stock [Line Items]
Reserved shares of common stock	3,995,876	3,561,104
Warrants to Purchase Common Stock [Member]
Class Of Stock [Line Items]
Reserved shares of common stock	300,564	128,663

Stock Option Plans - Additional Information (Detail) $ / shares in Units, $ in Thousands		12 Months Ended
	Sep. 04, 2015 $ / shares shares	Dec. 31, 2015 USD ($) Offering Period $ / shares shares	Dec. 31, 2014 USD ($) $ / shares shares	Dec. 31, 2013 USD ($) $ / shares shares	Dec. 31, 2012 shares	Jan. 01, 2015 shares	Jan. 31, 2014 shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense \| $		$ 2,375	$ 885	$ 622
Number of Shares, Granted		2,360,682
Weighted-Average Exercise Price, Options exercisable \| $ / shares		$ 5.56
Number of Shares, Options expected to vest		2,336,878
2007 Stock Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Maximum shares of common stock provided under stock incentive plan							1,275,211
Stock options vesting period		4 years
Stock options expiration period		10 years
Shares available for future grant		0	0
2014 Stock Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Maximum shares of common stock provided under stock incentive plan						1,000,000
Stock options vesting period		3 years
Shares available for future grant		540,950
Percentage of common stock outstanding stock on first day of the year						4.00%
Total intrinsic value of stock options exercised \| $		$ 0	$ 161	$ 15
Weighted-average per share grant date fair value of options granted \| $ / shares		$ 3.22	$ 3.33	$ 2.90
Unrecognized compensation cost related to unvested stock-based compensation arrangements \| $		$ 6,100
Weighted-average period of recognition of unrecognized compensation cost related to unvested stock-based compensation arrangements		2 years 10 months 17 days
Number of Shares, Options expected to vest		16,000
2014 Stock Incentive Plan [Member] \| CEO [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Shares, Granted					60,934
2014 Stock Incentive Plan [Member] \| Non Employee Awards [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average per share grant date fair value of options granted \| $ / shares	$ 2.71	$ 1.58
Stock-based compensation expense \| $		$ 173	$ 56	$ 85
Number of Shares, Granted	90,000	204,000	0	0
Weighted-Average Exercise Price, Options exercisable \| $ / shares	$ 4.71	$ 5.17
2014 Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Maximum shares of common stock provided under stock incentive plan		500,000				600,000
Percentage of common stock outstanding stock on first day of the year						1.00%
Stock-based compensation expense \| $		$ 27	$ 0
Offering period		6 months
Number of Offerings Per Year \| Offering Period		2

Stock Option Plans -Summary of Stock Option Activity for Employee and Nonemployee Awards under Plan (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Number of shares
Number of Shares, Outstanding	2,126,176
Number of Shares, Granted	2,360,682
Number of Shares, Exercised	(370,230)
Number of Shares, Forfeited	(661,702)
Number of Shares, Outstanding	3,454,926	2,126,176
Number of Shares, Options expected to vest	2,336,878
Number of Shares, Options exercisable	1,001,415
Weighted-Average Exercise Price
Weighted-Average Exercise Price, Outstanding	$ 4.97
Weighted-Average Exercise Price, Granted	5.66
Weighted-Average Exercise Price, Exercised	4.40
Weighted-Average Exercise Price, Forfeited	5.86
Weighted-Average Exercise Price, Outstanding	5.39	$ 4.97
Weighted-Average Exercise Price, Options expected to vest	5.32
Weighted-Average Exercise Price, Options exercisable	$ 5.56
Weighted-Average Remaining Contractual Life (Years)
Weighted-Average Remaining Contractual Life (Years)	8 years 10 months 24 days	6 years 8 months 12 days
Weighted-Average Remaining Contractual Life (Years), Options expected to vest - December 31, 2014	9 years 4 months 24 days
Weighted-Average Remaining Contractual Life (Years), Options exercisable - December 31, 2014	7 years 8 months 12 days
Aggregate Intrinsic Value
Aggregate Intrinsic Value, Outstanding		$ 2,701

Stock Option Plans - Schedule of Stock-based Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 2,375	$ 885	$ 622
Research and Development [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	795	317	284
General and Administrative [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 1,580	$ 568	$ 338

Stock Option Plans - Summary of Assumptions Used in Black-Scholes Option-Pricing Model for Stock Options Granted to Employees and Non Employees (Detail)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected life	6 years	6 years	6 years
Risk-free interest rate, minimum	1.45%	1.71%	1.09%
Risk-free interest rate, maximum	2.02%	2.00%	1.92%
Expected volatility, minimum	51.00%	54.00%	59.00%
Expected volatility, maximum	63.00%	60.00%	79.00%
Non Employee Awards [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected life	10 years	8 years	7 years
Risk-free interest rate, minimum	2.10%	1.86%	1.11%
Risk-free interest rate, maximum	2.25%	2.53%	2.86%
Expected volatility, minimum	60.00%	56.00%	56.00%
Expected volatility, maximum	61.00%	62.00%	79.00%

Fair Value Measurements - Additional Information (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Fair Value Disclosures [Abstract]
Money market fund investments	$ 75,325	$ 50,541

Fair Value Measurements - Summary of Financial Assets and Liabilities Measured on Recurring Basis at Fair Value (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	$ 75,325	$ 50,541
Fair Value, Measurements, Recurring [Member] \| Money Market Funds [Member] \| Carrying Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	75,325	50,541
Fair Value, Measurements, Recurring [Member] \| Money Market Funds [Member] \| Fair Value Measurements [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	$ 75,325	$ 50,541

Fair Value Measurements - Reconciliation of Company's Liabilities Measured at Fair Value on Recurring Basis Using Unobservable Inputs (Level 3) (Detail) - Significant Unobservable Inputs (Level 3) [Member] $ in Thousands	12 Months Ended
	Dec. 31, 2014 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Preferred stock warrant liability, Beginning balance	$ 928
Fair value reclassified to additional paid-in capital in connection with the completion of the IPO on April 15, 2014	(928)
Preferred Stock Warrant, Series B [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Preferred stock warrant liability, Beginning balance	4
Fair value reclassified to additional paid-in capital in connection with the completion of the IPO on April 15, 2014	(4)
Preferred Stock Warrant, Series C [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Preferred stock warrant liability, Beginning balance	386
Fair value reclassified to additional paid-in capital in connection with the completion of the IPO on April 15, 2014	(386)
Preferred Stock Warrant, Series D [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Preferred stock warrant liability, Beginning balance	538
Fair value reclassified to additional paid-in capital in connection with the completion of the IPO on April 15, 2014	$ (538)

Fair Value Measurements - Fair Value of Stock Warrants Calculated using Black-Scholes Assumptions (Detail)	12 Months Ended
	Dec. 31, 2013
Minimum [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Expected life	4 years
Risk-free interest rate	2.90%
Expected volatility	64.00%
Maximum [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Expected life	8 years
Risk-free interest rate	2.90%
Expected volatility	84.00%

Income Taxes - Significant Components of Company's Deferred Taxes (Detail) - USD ($)	Dec. 15, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Net operating loss carryforwards	$ 35,797	$ 29,442
Research and development credit carryforwards	2,066	1,715
Capitalized costs	3,977	3,503
Capitalized research and development costs	17,715	9,938
Other	903	422
Total deferred tax assets	60,458	45,020
Valuation allowance	(60,458)	(45,020)
Net deferred tax assets	$ 0	$ 0

Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 15, 2015
Operating Loss Carryforwards [Line Items]
Increase (decrease) in valuation allowance	$ 15.6	$ 7.6
Net operating loss carryforwards expiration year	2035	2034
Internal Revenue Service (IRS) [Member] \| Earliest Tax Year [Member]
Operating Loss Carryforwards [Line Items]
Tax year open to examination	2006
Internal Revenue Service (IRS) [Member] \| Latest Tax Year [Member]
Operating Loss Carryforwards [Line Items]
Tax year open to examination	2014
Federal [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards		$ 77.3	$ 93.7
Federal [Member] \| Research [Member]
Operating Loss Carryforwards [Line Items]
Research and development credit carryforwards		$ 1.2	1.4
Research and development tax credit carryforwards expiration year	2035	2034
State [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards		$ 58.1	74.1
State [Member] \| Research [Member]
Operating Loss Carryforwards [Line Items]
Research and development credit carryforwards		$ 0.8	$ 0.9
Research and development tax credit carryforwards expiration year	2030	2029

Income Taxes - Reconciliation of Income Tax Expense Computed at Statutory Federal Income Tax Rate to Income Taxes (Detail)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Federal income tax expense at statutory rate	34.00%	34.00%
State income tax, net of federal benefit	5.00%	4.50%
Permanent differences	(0.50%)	(3.70%)
Research and development credit	0.90%	0.80%
Stock compensation	(0.70%)	(0.90%)
Expiration of state net operating loss	(0.00%)	(1.70%)
Other	0.40%	(0.80%)
Change in valuation allowance	(39.10%)	(32.20%)
Effective income tax rate	0.00%	0.00%

Commitments - Additional Information (Detail) - USD ($) $ in Thousands		12 Months Ended
	Jul. 09, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating Leased Assets [Line Items]
Noncancelable operating lease expire date		Feb. 28, 2013
Noncancelable operating leases renewal option period		3 years
Deferred liability related to facility lease			$ 41
Lease amendment, commencement Date		Jul. 11, 2014
Lease termination date		Dec. 31, 2015
Noncancelable operating lease rent expenses		$ 920	$ 766	$ 598
Office Laboratory and Vivarium Space Facility Lease [Member]
Operating Leased Assets [Line Items]
Noncancelable operating lease expire date		Feb. 28, 2021
Noncancelable operating leases renewal option period	3 years
Extended Lease
Operating Leased Assets [Line Items]
Noncancelable operating lease expire date		Feb. 28, 2016

Commitments - Summary of Future Minimum Lease Payments under Non-cancelable Operating Leases (Detail) $ in Thousands	Dec. 31, 2015 USD ($)
Commitments And Contingencies Disclosure [Abstract]
2016	$ 575
2017	690
2018	738
2019	786
2020	830
2021	140
Total	$ 3,759

Licensing Agreements - Additional Information (Detail) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research and development	$ 7,157,000	$ 7,092,000	$ 6,678,000	$ 5,021,000	$ 4,701,000	$ 2,928,000	$ 2,648,000	$ 1,495,000	$ 25,948,000	$ 11,772,000	$ 9,700,000
Calando Pharmaceuticals, Inc. [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Bankruptcy proceedings, court where petition was filed									District of Delaware
Bankruptcy petition date filed									Mar. 03, 2015
Bankruptcy description									In March 2014, Calando entered Chapter 7 bankruptcy in the District of Delaware and, as a result, the intellectual property rights the Company has obtained from Calando are subject to potential risks that may arise in connection with bankruptcy.
Calando Product License Agreement [Member] \| Upon achievement of specified regulatory and commercial milestones [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payment									$ 32,800,000
Calando Platform License Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payment									17,800,000
Calando Platform License Agreement [Member] \| CRLX301 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payment									250,000
SUNY License Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research and development									36,000	30,000	25,000
MIT License Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research and development									$ 50,000	$ 10,000	$ 10,000

Retirement Plans - Additional Information (Detail) - Safe Harbor Plan [Member] - USD ($) $ in Thousands		12 Months Ended
	Jan. 01, 2010	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, employer matching contribution, percent of match	4.00%
Defined contribution plan, employer matching contribution		$ 264	$ 163	$ 145

Related Party Transactions - Additional Information (Detail) - USD ($)		12 Months Ended
	Apr. 01, 2014	Dec. 31, 2014	Dec. 31, 2013	Apr. 30, 2014
Related Party Transaction [Line Items]
Proceeds from sale of equipment	$ 30,000
IPO [Member]
Related Party Transaction [Line Items]
Convertible preferred stock, shares issued upon conversion				6,826,004
Affiliated Entity [Member]
Related Party Transaction [Line Items]
Fees recorded offsetting research and development expenses		$ 39,000	$ 84,000

Revenue - Additional Information (Detail) - USD ($)	3 Months Ended		12 Months Ended
Revenue - Additional Information (Detail) - USD ($)	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Revenue Recognition Milestone Method [Line Items]
Revenue	$ 33,000	$ 47,000		$ 80,000	$ 6,000
Material Transfer Agreement [Member]
Revenue Recognition Milestone Method [Line Items]
Revenue			$ 0	61,000	$ 6,000
Material Transfer Agreement One [Member]
Revenue Recognition Milestone Method [Line Items]
Revenue				$ 19,000

Quarterly Financial Data (Unaudited) - Schedule of Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Quarterly Financial Information Disclosure [Abstract]
Revenue							$ 33	$ 47		$ 80	$ 6
Operating expenses:
Research and development	$ 7,157	$ 7,092	$ 6,678	$ 5,021	$ 4,701	$ 2,928	2,648	1,495	$ 25,948	11,772	9,700
General and administrative	2,872	2,954	2,717	2,681	2,607	2,441	2,029	1,510	11,224	8,587	6,166
Total operating expenses	10,029	10,046	9,395	7,702	7,308	5,369	4,677	3,005	37,172	20,359	15,866
Other income (expense):
Interest income	2	4	1	3	4	2	2	1	10	9	2
Interest expense	(689)	(509)	(513)	(721)	(163)	(191)	(268)	(461)	(2,432)	(1,083)	(1,487)
Loss on extinguishment of debt							(2,493)			(2,493)
Decrease in value of preferred stock warrant liability								504		504	202
Total other income (expense), net	(687)	(505)	(512)	(718)	(159)	(189)	(2,759)	44	(2,422)	(3,063)	(1,283)
Net loss attributable to common stockholders	$ (10,716)	$ (10,551)	$ (9,907)	$ (8,420)	$ (7,467)	$ (5,558)	$ (7,403)	$ (2,914)	$ (39,594)	$ (23,342)	$ (17,143)
Net loss per share attributable to common stockholders:
Basic and diluted	$ (0.39)	$ (0.39)	$ (0.37)	$ (0.41)	$ (0.37)	$ (0.28)	$ (0.44)	$ (3.70)	$ (1.56)	$ (1.60)	$ (25.05)
Weighted-average common shares outstanding:
Basic and diluted	27,346,780	27,307,103	26,690,673	20,350,557	20,125,009	20,124,574	16,883,716	786,986	25,431,332	14,548,516	684,330