Daré Bioscience (DARE) S-1 20 Mar 15 IPO registration Financial data

Document_and_Entity_Informatio

Document and Entity Information	12 Months Ended
	Dec. 31, 2014
Document And Entity Information [Abstract]
Document Type	S-1
Amendment Flag	FALSE
Document Period End Date	31-Dec-14
Trading Symbol	CERU
Entity Registrant Name	CERULEAN PHARMA INC.
Entity Central Index Key	1401914
Entity Filer Category	Non-accelerated Filer

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Current assets:
Cash and cash equivalents	$51,174	$5,488
Accounts receivable, prepaid expenses, and other current assets	1,662	959
Total current assets	52,836	6,447
Property and equipment — Net	342	245
Other assets	215	135
Total	53,393	6,827
Current liabilities:
Current portion of loan payable	3,124	3,134
Convertible promissory notes payable to shareholders		8,824
Accounts payable	1,255	914
Accrued expenses	3,648	2,274
Other liabilities	34
Total current liabilities	8,061	15,146
Long-term liabilities:
Loan payable — net of current portion		3,124
Preferred stock warrant liability		928
Noncurrent accrued interest		391
Other	7	12
Total long-term liabilities	7	4,455
Redeemable convertible preferred stock (Note 8)		81,525
Commitments (Note 13)
Stockholders’ equity (deficit):
Preferred stock, $0.01 par value; 5,000,000 shares authorized, no shares issued or outstanding	0	0
Common stock, $0.0001 par value; 120,000,000 shares authorized, 20,125,049 and 785,531 shares issued and outstanding at December 31, 2014 and 2013, respectively	2
Additional paid-in capital	167,104	4,140
Accumulated deficit	-121,781	-98,439
Total stockholders’ equity (deficit)	45,325	-94,299
Total	$53,393	$6,827

Consolidated_Balance_Sheets_Pa

Consolidated Balance Sheets (Parenthetical) (USD $)	Dec. 31, 2014	Dec. 31, 2013
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	$0.00	$0.00
Common stock, shares authorized	120,000,000	120,000,000
Common stock, shares issued	20,125,049	785,531
Common stock, shares outstanding	20,125,049	785,531

Consolidated_Statements_of_Ope

Consolidated Statements of Operations (USD $)	1 Months Ended	3 Months Ended								12 Months Ended
In Thousands, except Share data, unless otherwise specified	Apr. 30, 2014	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Statement [Abstract]
Revenue				$33	$47	$6				$80	$6	$625
Operating expenses:
Research and development		4,701	2,928	2,648	1,495	1,440	1,586	3,195	3,479	11,772	9,700	15,807
General and administrative		2,607	2,441	2,029	1,510	1,575	1,227	1,392	1,972	8,587	6,166	6,393
Total operating expenses		7,308	5,369	4,677	3,005	3,015	2,813	4,587	5,451	20,359	15,866	22,200
Other income (expense):
Interest income		4	2	2	1	1			1	9	2	2
Interest expense		-163	-191	-268	-461	-430	-378	-326	-353	-1,083	-1,487	-567
Loss on extinguishment of debt	-2,493			-2,493						-2,493
Decrease in value of preferred stock warrant liability					504	-42	-7	20	231	504	202	39
Total other income (expense) — net		-159	-189	-2,759	44	-471	-385	-306	-121	-3,063	-1,283	-526
Net loss										-23,342	-17,143	-22,101
Accretion of redeemable convertible preferred stock												-73
Net loss attributable to common stockholders		($7,467)	($5,558)	($7,403)	($2,914)	($3,480)	($3,198)	($4,893)	($5,572)	($23,342)	($17,143)	($22,174)
Net loss per share attributable to common stockholders:
Basic and diluted		($0.37)	($0.28)	($0.44)	($3.70)	($4.45)	($4.40)	($7.96)	($9.09)	($1.60)	($25.05)	($36.39)
Weighted-average common shares outstanding:
Basic and diluted		20,125,009	20,124,574	16,883,716	786,986	782,335	726,987	614,662	612,836	14,548,516	684,330	609,344

Consolidated_Statement_of_Rede

Consolidated Statement of Redeemable Preferred Stock and Stockholders' Equity (Deficit) (USD $)	Total	Series D Convertible Preferred Stock [Member]	IPO [Member]	Redeemable Convertible Preferred Stock [Member]	Redeemable Convertible Preferred Stock [Member]	Common Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]
In Thousands, except Share data	USD ($)	USD ($)	USD ($)	USD ($)	Series D Convertible Preferred Stock [Member]	USD ($)	IPO [Member]	USD ($)	IPO [Member]	USD ($)
					USD ($)				USD ($)
Redeemable convertible preferred stock, Beginning balance at Dec. 31, 2011				$70,751
Beginning balance at Dec. 31, 2011	-58,397							798		-59,195
Redeemable convertible preferred stock, Beginning balance, shares at Dec. 31, 2011				71,374,896
Beginning balance, shares at Dec. 31, 2011						609,041
Exercise of stock options	3							3
Exercise of stock options, shares						904
Sale of convertible preferred stock					12,927
Sale of convertible preferred stock, shares					15,662,650
Stock-based compensation	529							529
Accretion of issuance costs to redemption value	-73			73				-73
Net loss	-22,101									-22,101
Redeemable convertible preferred stock, Ending balance at Dec. 31, 2012				83,751
Ending balance at Dec. 31, 2012	-80,039							1,257		-81,296
Redeemable convertible preferred stock, Ending balance, shares at Dec. 31, 2012				87,037,546
Ending balance, shares at Dec. 31, 2012						609,945
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
Redeemable convertible preferred stock, Ending balance at Dec. 31, 2013	81,525	27,521		81,525
Ending balance at Dec. 31, 2013	-94,299							4,140		-98,439
Redeemable convertible preferred stock, Ending balance, shares at Dec. 31, 2013	85,207,356	33,158,272		85,207,356
Ending balance, shares at Dec. 31, 2013						785,531
Exercise of stock options	140							140
Exercise of stock options, shares	41,566					41,566
Stock-based compensation	885							885
Issuance of Common Stock from initial public offering	59,862					1		59,861
Issuance of Common Stock from initial public offering, 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 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

Consolidated_Statement_of_Rede1

Consolidated Statement of Redeemable Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) (USD $)	12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2012	Dec. 31, 2013
Preferred stock, par value	$0.01		$0.01
Common stock, par value	$0.00		$0.00
Stock issuance costs	$187
IPO [Member]
Stock issuance costs	7,126
Minimum [Member]
Conversion price, per share			$14.51
Maximum [Member]
Conversion price, per share			$39.21
Series D Convertible Preferred Stock [Member]
Issuance/sale of stock, price per share		$0.83
Stock issuance costs		$73

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash flows from operating activities:
Net loss	($23,342)	($17,143)	($22,101)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	885	622	529
Noncash rent expense	29	-1	-68
Change in carrying value of preferred stock warrant liability	-504	-202	-39
Depreciation and amortization	126	197	346
Loss (gain) on disposal of property and equipment	-28	7	2
Loss on extinguishment of debt	2,493
Noncash interest expense	416	588	61
Changes in operating assets and liabilities:
Accounts receivable, prepaid expenses and other current assets	-713	-229	-61
Accounts payable	341	14	-163
Accrued expenses	1,236	-467	489
Net cash used in operating activities	-19,061	-16,614	-21,005
Cash flows from investing activities:
Purchases of property and equipment	-225	-7	-180
Proceeds from sale of property and equipment	40
Net cash used in investing activities	-185	-7	-180
Cash flows from financing activities:
Proceeds from sale of common stock	140	35	3
Proceeds from issuance of convertible promissory notes	8,500	8,824
Proceeds from initial public offering, net	59,862
Proceeds from loans payable			10,000
Payments on capital lease			-3
Payments on loans payable	-3,348	-3,084	-376
Cash paid for debt issuance costs	-222	-373	-4
Proceeds from sale of redeemable convertible preferred stock, net of issuance costs			12,927
Net cash provided by financing activities	64,932	5,402	22,547
Net increase (decrease) in cash and cash equivalents	45,686	-11,219	1,362
Cash and cash equivalents — Beginning of year	5,488	16,707	15,345
Cash and cash equivalents — End of year	51,174	5,488	16,707
Supplemental disclosures of noncash investing and financing activities:
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
Accretion of redeemable convertible preferred stock to redemption value			73
Fair value of preferred stock warrants issued in connection with debt			360
Supplemental cash flow information — Interest paid	$400	$664	$507

Nature_of_Business_and_Operati

Nature of Business and Operations	12 Months Ended
	Dec. 31, 2014
Accounting Policies [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 Cambridge, 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. To date, operations of the Australia subsidiary have been immaterial.
	The Company's operations to date have consisted primarily of raising capital, product research and development, and initial market development. Accordingly, the Company is considered to be in the development stage at December 31, 2014.
	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 $121.8 million at December 31, 2014. The Company has financed its operations primarily through private placements of its preferred stock, proceeds from borrowings, and an initial public offering completed in 2014. 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. The Company expects to continue to incur significant expenses and increasing operating losses for at least several years.
	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 preparation for the IPO, the Company’s board of directors and stockholders approved a 1-for-14.5074 reverse stock split of the Company’s common stock effective March 31, 2014. All share and per share amounts in the consolidated financial statements contained herein and notes thereto have been retroactively adjusted, where necessary, to give effect to this reverse stock split. 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. The significant increase in shares outstanding in April 2014 is expected to impact the year-over-year comparability of the Company’s net loss per share calculations in future periods.
	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_Policie

Significant Accounting Policies	12 Months Ended
	Dec. 31, 2014
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 (Cambridge, 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, 2014 and 2013, the Company has restricted cash of $117,000 representing a letter of credit for the Company’s facility lease that is scheduled to expire in February 2016. The letter of credit is secured by certificates of deposit that renew monthly. 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, 2014 and 2013, 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 classifies redeemable convertible preferred stock that is 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 is being increased by periodic accretion to its redemption value. In the absence of retained earnings these accretion charges are recorded against additional paid-in capital, if any, and then to accumulated deficit. The Company amortizes 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 Company’s IPO in April 2014.
	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, 2014 and 2013, the Company has not identified any significant uncertain tax positions.
	Guarantees and Indemnification — As permitted under Delaware law, the Company indemnifies its officers, directors, and 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 — In August 2014 Financial Accounting Standards Board (the “FASB”) issued Accounting Standards Update (“ASU”) 2014-15, “Disclosure of Uncertainties About an Entity’s Ability to Continue as a Going Concern” (“ASU 2014-15”). ASU 2014-15 requires management to evaluate, at each annual and interim reporting period, whether there are conditions or events that raise substantial doubt about the entity’s ability to continue as a going concern and provide related disclosures. ASU 2014-15 is effective for annual and interim reporting periods beginning January 1, 2017 and is not expected to have a material impact on the Company’s consolidated financial statements.
	In June 2014, the FASB issued ASU No. 2014-10, “Development Stage Entities: Elimination of Certain Financial Reporting Requirements, Including an Amendment to Variable Interest Entities Guidance in Topic 810, Consolidation.” This accounting standard eliminates all incremental financial reporting requirements from U.S. GAAP for development stage entities, thereby improving financial reporting by reducing the cost and complexity associated with providing such information. The Company will no longer be required to present inception-to-date information. This ASU is effective on a prospective basis for annual and interim reporting periods beginning on or after December 15, 2014, with early adoption permitted. The Company elected to early adopt the ASU starting with its June 30, 2014 financial statements and, accordingly, has not included inception to date information it the accompanying financial statements.

Net_Loss_Per_Share_Attributabl

Net Loss Per Share Attributable to Common Stockholders	12 Months Ended
	Dec. 31, 2014
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,
			2014			2013			2012
	Net loss		$	(23,342	)	$	(17,143	)	$	(22,101	)
	Accretion of preferred stock issuance costs to redemption value			—			—			(73	)
	Net loss attributable to common stockholders — basic and diluted		$	(23,342	)	$	(17,143	)	$	(22,174	)
	Weighted-average number of common shares — basic and diluted			14,548,516			684,330			609,344
	Net loss per share attributable to common stockholders — basic and diluted		$	(1.60	)	$	(25.05	)	$	(36.39	)
	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,
			2014			2013			2012
	Options to purchase common stock			2,126,176			1,062,694			1,046,178
	Warrants to purchase redeemable convertible preferred stock			—			128,663			128,663
	Warrants to purchase common stock			128,663			—			—
	Redeemable convertible preferred stock			—			6,826,004			6,992,694
	Convertible notes payable			—			754,785			—

Property_and_Equipment

Property and Equipment	12 Months Ended
	Dec. 31, 2014
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,
			2014			2013
	Laboratory equipment		$	1,163		$	1,246
	Computer equipment			260			183
	Office furniture and equipment			292			257
	Leasehold improvements			117			91
				1,832			1,777
	Less accumulated depreciation and amortization			(1,490	)		(1,532	)
	Property and equipment, net		$	342		$	245
	Depreciation and amortization expense for the years ended December 31, 2014, 2013 and 2012 was $126,000, $197,000 and $346,000, respectively.

Accrued_Expenses

Accrued Expenses	12 Months Ended
	Dec. 31, 2014
Payables And Accruals [Abstract]
Accrued Expenses	5	ACCRUED EXPENSES
	Accrued expenses consist of the following (in thousands):
			As of December 31,
			2014		2013
	Accrued expenses		$	663	$	379
	Accrued clinical trial costs			848		610
	Accrued contract manufacturing expenses			580		433
	Accrued compensation and benefits			983		618
	Accrued interest			574		234
	Total accrued expenses		$	3,648	$	2,274

Convertible_Notes_Payable_to_S

Convertible Notes Payable to Shareholders	12 Months Ended
	Dec. 31, 2014
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 11) 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

Loan Agreements	12 Months Ended
	Dec. 31, 2014
Debt Disclosure [Abstract]
Loan Agreements	7	LOAN AGREEMENTS
	In August 2008, the Company entered into a Loan and Security Agreement (the “Loan Agreement”) with a bank to borrow up to $1,500,000 in one or more advances to finance certain equipment purchases made by the Company through May 31, 2009. In September 2008, the Company received its only advance totaling $695,000 and issued a note payable to the bank. No additional advances were made. The note was payable over a 48-month period in equal principal payments, plus interest on the outstanding balance, fixed at the 8.75%. The note was secured by a security interest in the specific equipment financed. In September 2012, the Company paid the remaining balance in accordance with the original repayment schedule.
	In connection with the Loan Agreement, the Company issued the bank a warrant to purchase 15,000 shares of the Company’s Series B Preferred Stock at an exercise price of $2.00 per share. The warrant was immediately exercisable and expires 10 years from the date of grant. The value of the warrant was recorded as a discount to the note payable and was amortized to interest expense using the effective interest method over the 48-month repayment term. The Company estimated the fair value of the warrant on the grant date to be $25,000 using the Black-Scholes option-pricing model with the following assumptions: volatility of 79%, contractual term of 10 years, risk-free interest rate of 3.89%, 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 11) until their conversion to common stock warrants to purchase 1,695 shares of common stock upon the completion of the IPO in April 2014.
	In December 2011, the Company entered into a loan and security agreement with Lighthouse Capital Partners VI, L.P. (“Lighthouse Capital”) to borrow up to $10,000,000 in one or more advances by December 31, 2012. Debt proceeds are available to the Company to fund research and development activities and other general corporate purposes. The Company granted Lighthouse Capital a first priority security interest in all unsecured present and future assets, other than intellectual property, and the Company entered into a negative pledge agreement with the lender, whereby the Company agrees not to grant a security interest in or encumber any of the Company’s intellectual property. The Company also has restrictions on its ability to obtain additional debt that is not permitted under the agreement. In both March 2012 and August 2012, the Company borrowed $5,000,000 under the loan and security agreement, for a total of $10,000,000. This amount was being repaid over 36 months beginning on December 1, 2012, at an interest rate of 8.25%.
	In addition, the Company is required to make an additional interest payment in the amount of $600,000 at the end of the loan term. The amount is being accrued over the loan term as interest expense. The amount accrued as of December 31, 2014 was $574,000 and is included in accrued expense in the accompanying balance sheet.  As of December 31, 2013 the amount accrued was $391,000, and was included as non-current accrued interest expense in the accompanying balance sheet. The minimum future principal payments are as follows (in thousands):
	Year Ending December 31,
	2015		$	3,321
	Unamortized discount relating to warrants			(197	)
	Total			3,124
	Less current portion			(3,124	)
	Long-term portion		$	-
	In January 2015, the Company repaid in full the amount outstanding under the Lighthouse Capital loan with the proceeds from a new loan (see Note 18).
	In connection with the loan and security agreement with Lighthouse Capital, the Company issued the lender 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. The warrant was immediately exercisable for 29,067 shares at the date of issue and expires 10 years from the date of issue (December 2021). The exercisable shares increased in March 2012 and August 2012 as the Company borrowed under the loan and security agreement. At December 31, 2014 and 2013, 66,436 shares were exercisable. The fair value of the warrant was estimated on the date of issue for the exercisable shares at that date and the fair value of each increment was estimated on the date the shares became exercisable, using the Black-Scholes option-pricing model. The Company estimated the fair value of the warrant for shares exercisable on the issue date in December 2011 and incremental shares exercisable in March 2012 and August 2012 to be $284,000, $182,000 and $178,000, respectively. The following table shows the Black-Scholes assumptions used to value the preferred stock warrants in connection with the loan and security agreement on the respective dates:
			Series D Preferred Stock Warrants
			December 2011			Mar-12			Aug-12
	Contractual life		10 years			9.69 years			9.29 years
	Volatility rate			80	%		80	%		80	%
	Risk-free interest rate			1.98	%		2.17	%		1.68	%
	Expected dividends			—			—			—
	The value of the warrant is recorded as a discount to the loan and is being amortized to interest expense using the effective interest method over the 36-month repayment term.
	The Company determined the fair value of the warrant at the end of each subsequent reporting period using the Black-Scholes option pricing model (see Note 11) until their conversion to warrants to purchase 66,436 shares of common stock upon the completion of the IPO in April 2014.

Redeemable_Convertible_Preferr

Redeemable Convertible Preferred Stock	12 Months Ended
	Dec. 31, 2014
Temporary Equity Disclosure [Abstract]
Redeemable Convertible Preferred Stock	8	REDEEMABLE CONVERTIBLE PREFERRED STOCK
	In connection with the closing of the IPO in April 2014, all of the Company’s outstanding convertible preferred stock automatically converted to common stock resulting in an additional 6,826,004 shares of common stock of the Company becoming outstanding.
	As of December 31, 2013, preferred stock consisted of the following (in thousands, except share data):
			Preferred		Issuance Date	Preferred Shares		Redemption		Carrying Value
			Shares			Issued and		Value /Liquidation
			Authorized			Outstanding		Preference
	Seed			2,500,000	Dec-06		2,500,000	$	2,000	$	2,000
	Series A			9,307,692	May-07		9,307,692		12,100		12,100
	Series B			4,077,500	Dec-07		3,562,500		7,125		7,125
	Series B-1			5,000,000	Jul-09		4,842,500		9,685		9,685
	Series C			33,310,787	November 2010 and June 2011		31,836,392		23,559		23,094
	Series D			34,698,793	December 2011 and November 2012		33,158,272		27,521		27,521
				88,894,772			85,207,356	$	81,990	$	81,525

Stockholders_Equity_Deficit

Stockholder's Equity (Deficit)	12 Months Ended
	Dec. 31, 2014
Stockholders Equity Note [Abstract]
Stockholder's Equity (Deficit)	9	STOCKHOLDERS’ EQUITY (DEFICIT)
	Common Stock — As discussed in Note 1, 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, 2014 and 2013:
			As of December 31,
			2014		2013
	Redeemable convertible preferred stock			—		6,954,691
	Warrants to purchase common stock			128,663		—
	Common stock options			3,561,104		1,201,770
	Total			3,689,767		8,156,461

Stock_Option_Plans

Stock Option Plans	12 Months Ended
	Dec. 31, 2014
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock Option Plans	10	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, 2014, there were no shares available for future grant under the 2007 Plan.  At December 31, 2013, there were 139,076 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. As of December 31, 2014, there were 1,434,928 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, 2014 is presented below:
			Number of			Weighted-		Weighted-		Aggregate
			Shares			Average		Average		Intrinsic
						Exercise		Remaining		Value
						Price		Contractual
								Life (Years)
	Outstanding — January 1, 2014			1,062,694		$	3.98		7.2	$	7,028
	Granted			1,138,170			5.99
	Exercised			(41,566	)		3.36
	Forfeited			(33,122	)		4.85
	Outstanding — December 31, 2014			2,126,176		$	4.97		6.7	$	2,701
	Options expected to vest — December 31, 2014			859,690		$	5.46		9.2	$	1,105
	Options exercisable — December 31, 2014			786,623		$	4.41		3.9	$	1,541
	The total intrinsic value of stock options exercised in the years ended December 31, 2014, 2013 and 2012 was $161,000, $15,000, and $0, respectively.
	The weighted-average per share grant date fair value of options granted during 2014, 2013 and 2012 was $3.33, $2.90, and $2.61, respectively.
	The Company has recorded stock-based compensation expense of $885,000, $622,000 and $529,000 during the years ended December 31, 2014, 2013 and 2012, respectively, which is based on the number of awards ultimately expected to vest. As of December 31, 2014, there was $2.2 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 3.02 years at December 31, 2014.
	Stock-based compensation expense recorded as research and development and general and administrative expenses is as follows (in thousands):
			As of December 31,
			2014			2013		2012
	Research and development		$	317		$	284	$	187
	General and administrative			568			338		342
	Total		$	885		$	622	$	529
	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, 2014, 2013 and 2012 are as follows:
			December 31,
			2014		2013	2012
	Expected life		6 years		6 years	6 years
	Risk-free interest rate		1.71%-2.00%		1.09%-1.92%	0.83%-1.12%
	Expected volatility		54%-60%		59%-79%	77%-79%
	Expected dividend rate		—%		—%	—%
	The Company recorded stock-based compensation expense related to nonemployee awards of $56,000, $85,000 and $39,000 for the years ended December 31, 2014, 2013 and 2012, 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, 2014, 2013 and 2012 were as follows:
			December 31,
			2014		2013	2012
	Expected life		8 years		7 years	6 years
	Risk-free interest rate		1.86%-2.53%		1.11%-2.86%	0.99%-2.05%
	Expected volatility		56%-62%		56%-79%	76%-79%
	Expected dividend rate		—%		—%	—%
	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 2013 and 2012, the Company granted to the Company’s Chief Executive Officer (“CEO”) options to purchase up to 53,489 and 56,053 shares of common stock, respectively. The vesting of these awards was contingent upon either (i) a change of control at a minimum price per share or (ii) the registration of the Company’s common stock under the Securities Exchange Act of 1934 and the stock being quoted, listed or traded on an over-the-counter market or national securities exchange at a certain price per share.  The CEO resigned in October 2014 and although the Company completed its IPO in April 2014, the minimum price per share required was never achieved therefore these awards will not vest.  Also in 2012, the Company granted options to purchase 60,934 common shares to a second Company 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, 2014.  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.  The Company did not offer shares to its employees under the 2014 ESPP during the year ended December 31, 2014.

Fair_Value_Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2014
Fair Value Disclosures [Abstract]
Fair Value Measurements	11	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, 2014 and 2013, are money market fund investments of $50,541,000 and $5,233,000, 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, 2014 and 2013, is as follows (in thousands):
						Fair Value Measurements Using
			Carrying			Quoted Prices in			Significant			Significant
						Active Markets			Other			Unobservable
						for Identical			Observable			Inputs
						Assets			Inputs
			Value			(Level 1)			(Level 2)			(Level 3)
	31-Dec-14
	Money market funds		$	50,541		$	—		$	50,541		$	—
	31-Dec-13
	Money market funds		$	5,233		$	—		$	5,233		$	—
	Preferred stock warrant liability			928			—			—			928
	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, 2014 and 2013, 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, 2012		$	7		$	500		$	623		$	1,130
	Decrease in fair value recorded in other income			(3	)		(114	)		(85	)		(202	)
	Balance — December 31, 2013			4			386			538			928
	Fair value reclassified to additional paid-in capital in connection			(4	)		(386	)		(538	)		(928	)
	with the IPO on April 15, 2014
	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:
			31-Dec-13
	Expected life		4-8 years
	Risk-free interest rate			2.9	%
	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.

Income_Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Income Taxes	12	INCOME TAXES
	Significant components of the Company’s deferred taxes at December 31, 2014 and 2013 are as follows:
			2014			2013
	Net operating loss carryforwards		$	29,442		$	25,696
	Research and development credit carryforwards			1,715			1,525
	Capitalized costs			3,503			3,067
	Capitalized research and development costs			9,938			6,992
	Other			422			220
	Total deferred tax assets			45,020			37,500
	Valuation allowance			(45,020	)		(37,500	)
	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 2014 and 2013 by approximately $7.6 million and $7.1 million, respectively, due to the increase in the deferred tax assets by the same amount.
	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,
			2014			2013
	Federal income tax expense at statutory rate			34	%		34	%
	State income tax, net of federal benefit			4.5	%		5	%
	Permanent differences			(3.7	%)		0.2	%
	Research and development credit			0.8	%		1.4	%
	Stock compensation			(0.9	%)		(1.1	%)
	Expiration of state net operating loss			(1.7	%)		(4.2	%)
	Other			(0.8	%)		0.2	%
	Change in valuation allowance			(32.2	%)		(35.5	%)
	Effective income tax rate			0	%		0	%
	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, 2014 and 2013, the Company has not identified any significant uncertain tax positions.

Commitments

Commitments	12 Months Ended
	Dec. 31, 2014
Commitments And Contingencies Disclosure [Abstract]
Commitments	13	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 which expires concurrent with the lease agreement in February 2016. The lease agreement and amendment include base rent escalation over the lease term, therefore, the Company is amortizing the cost of the lease on a straight-line basis over the lease term and the resulting deferred liability recorded in other current and long-term liabilities as of December 31, 2014 and 2013 was $41,000 and $12,000, respectively. Rent expense under this lease was $766,000, $598,000 and $517,000 for the years ended December 31, 2014, 2013 and 2012, respectively. 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, including the three-year extension, under the non-cancelable operating lease are as follows (in thousands):
			Operating
	Years Ending December 31,		Leases
	2015			954
	2016			160
	Total		$	1,114

Licensing_Agreements

Licensing Agreements	12 Months Ended
	Dec. 31, 2014
Research And Development Expense [Abstract]
Licensing Agreements	14	LICENSING AGREEMENTS
	Massachusetts Institute of Technology License — The Company’s license agreement with the Massachusetts Institute of Technology (“MIT”), as amended, requires the Company to pay MIT nonrefundable annual license maintenance fees that increase each year beginning in 2015 through 2020 and remain constant thereafter. The annual license fee is not material in any individual year. In addition, the Company may be required to pay milestone payments and/or product royalties in the event future partner collaborations or product sales incorporate technology covered by this license agreement. In connection with this agreement, the Company recorded research and development expense for annual maintenance fees of $10,000 each in the years ended December 31, 2014, 2013 and 2012.
	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 was required to pay Calando a $250,000 clinical development milestone upon initiation of a Phase 1 clinical trial for CRLX301. In addition, the Company may be required to pay Calando up to $17.8 million upon the achievement of specified regulatory and commercial milestones and pay royalty payments ranging from low-to mid-single digits on commercial sales.
	In connection with this agreement, the Company recorded research and development expense of $250,000 for the year ended December 31, 2014 upon initiation of the Phase 1 clinical trial for CRLX301 in December 2014.
	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 $30,000, $25,000, and $10,000 for the years ended December 31, 2014, 2013 and 2012, respectively.

Retirement_Plans

Retirement Plans	12 Months Ended
	Dec. 31, 2014
Compensation And Retirement Disclosure [Abstract]
Retirement Plans	15	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 $163,000, $145,000 and $165,000 to the 401(k) Plan for the years ended December 31, 2014, 2013 and 2012, respectively.

Related_Party_Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2014
Related Party Transactions [Abstract]
Related Party Transactions	16	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 Notes 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.

Revenue

Revenue	12 Months Ended
	Dec. 31, 2014
Revenues [Abstract]
Revenue	17	REVENUE
	The Company entered into a material transfer agreement in February 2012 with a biopharmaceutical company and amended the agreement in March 2012. The terms of the agreement provided revenue in exchange for conducting research using the Company’s proprietary technology and the pharmaceutical company’s proprietary compounds. The Company received $625,000 under this agreement and recognized this amount as revenue during 2012, the period when the research work was performed and all deliverables were completed.
	In October 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 $61,000 and $6,000 for the years ended December 31, 2014 and 2013, respectively, in connection with this material transfer agreement.
	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.

Subsequent_Events

Subsequent Events	12 Months Ended
	Dec. 31, 2014
Subsequent Events [Abstract]
Subsequent Events	18	SUBSEQUENT EVENTS
	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., or Hercules, the proceeds of which were used to repay the Company’s existing term loan facility with Lighthouse Capital and for general corporate and working capital purposes.
	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 provides for up to three separate borrowings, the first of which was funded in the amount of $15.0 million on the Closing Date. The second borrowing of up to $5.0 million may be drawn by the Company, subject to the satisfaction of customary funding conditions, on or prior to December 15, 2015, provided that the Company meets certain clinical milestones. The third borrowing of up to $6.0 million (the “Term C Loan Advance”) may be drawn, at no less than $3.0 million per draw and subject to the satisfaction of customary funding conditions, on or after September 30, 2015 but before December 15, 2015, provided that between the Closing Date and December 15, 2015, the Company has received net cash proceeds of at least $40.0 million from the issuance and sale by the Company of its equity securities and/or upfront cash payments from one or more strategic corporate partnerships.
	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 provides for interest-only payments on a monthly basis until December 31, 2015. The interest only period may be extended at the Company’s option for a three month period if the Company attains certain clinical milestones, and for an additional three month period if the Company attains certain clinical milestones and receives net cash proceeds of at least $30.0 million from the issuance and sale by the Company of its equity securities and/or upfront cash payments from one or more strategic corporate partnerships. Thereafter, amortization 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 (i) 3.0% if such prepayment occurs within twelve months of the Closing Date, (ii) 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 (iii) 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. At the end of the loan term (whether at maturity, by prepayment in full or otherwise), the Company shall make a final payment to the lender in the amount of 6.70% of the aggregate original principal amount advanced by the lender.
	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 initially exercisable for 137,521 shares of common stock. On such date (if any) as a Term C Loan Advance is made to the Company, the warrant shall automatically become exercisable for an additional 34,380 shares of common stock. The exercise price and the number of shares are subject to adjustment upon a merger event, reclassification of the shares of Common Stock, subdivision or combination of the shares of common stock or certain dividend payments. The warrant is exercisable until January 8, 2020.
	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.

Quarterly_Financial_Data_Unaud

Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Data (Unaudited)	19.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, 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
		Year Ended December 31, 2013
		First Quarter			Second Quarter			Third Quarter			Fourth Quarter
	Revenue	$	—		$	—		$	—		$	6
	Operating expenses:
	Research and development		3,479			3,195			1,586			1,440
	General and administrative		1,972			1,392			1,227			1,575
	Total operating expenses		5,451			4,587			2,813			3,015
	Other income (expense):
	Interest income		1			—			—			1
	Interest expense		(353	)		(326	)		(378	)		(430	)
	Loss on extinguishment of debt		—			—			—			—
	Decrease in value of preferred stock warrant liability		231			20			(7	)		(42	)
	Total other income (expense) — net		(121	)		(306	)		(385	)		(471	)
	Net loss attributable to common stockholders	$	(5,572	)	$	(4,893	)	$	(3,198	)	$	(3,480	)
	Net loss per share attributable to common stockholders:
	Basic and diluted	$	(9.09	)	$	(7.96	)	$	(4.40	)	$	(4.45	)
	Weighted-average common shares outstanding:
	Basic and diluted		612,836			614,662			726,987			782,335

Significant_Accounting_Policie1

Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Use of Estimates	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	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	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 (Cambridge, MA) and Australia (Sydney, NSW).  There is no revenue generated or long-lived assets located within the Australian location.
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	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	Restricted Cash — At December 31, 2014 and 2013, the Company has restricted cash of $117,000 representing a letter of credit for the Company’s facility lease that is scheduled to expire in February 2016. The letter of credit is secured by certificates of deposit that renew monthly. The restricted cash is included within other assets in the balance sheet.
Property and Equipment	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	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, 2014 and 2013, the Company has not recorded an impairment charge for its long-lived assets.
Revenue Recognition	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 — 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 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	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	Redeemable Convertible Preferred Stock — The Company classifies redeemable convertible preferred stock that is 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 is being increased by periodic accretion to its redemption value. In the absence of retained earnings these accretion charges are recorded against additional paid-in capital, if any, and then to accumulated deficit. The Company amortizes 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 Company’s IPO in April 2014.
Stock-Based Compensation	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	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	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, 2014 and 2013, the Company has not identified any significant uncertain tax positions.
Guarantees and Indemnification	Guarantees and Indemnification — As permitted under Delaware law, the Company indemnifies its officers, directors, and 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	Recent Accounting Pronouncements — In August 2014 Financial Accounting Standards Board (the “FASB”) issued Accounting Standards Update (“ASU”) 2014-15, “Disclosure of Uncertainties About an Entity’s Ability to Continue as a Going Concern” (“ASU 2014-15”). ASU 2014-15 requires management to evaluate, at each annual and interim reporting period, whether there are conditions or events that raise substantial doubt about the entity’s ability to continue as a going concern and provide related disclosures. ASU 2014-15 is effective for annual and interim reporting periods beginning January 1, 2017 and is not expected to have a material impact on the Company’s consolidated financial statements.
	In June 2014, the FASB issued ASU No. 2014-10, “Development Stage Entities: Elimination of Certain Financial Reporting Requirements, Including an Amendment to Variable Interest Entities Guidance in Topic 810, Consolidation.” This accounting standard eliminates all incremental financial reporting requirements from U.S. GAAP for development stage entities, thereby improving financial reporting by reducing the cost and complexity associated with providing such information. The Company will no longer be required to present inception-to-date information. This ASU is effective on a prospective basis for annual and interim reporting periods beginning on or after December 15, 2014, with early adoption permitted. The Company elected to early adopt the ASU starting with its June 30, 2014 financial statements and, accordingly, has not included inception to date information it the accompanying financial statements.

Significant_Accounting_Policie2

Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2014
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_Attributabl1

Net Loss Per Share Attributable to Common Stockholders (Tables)	12 Months Ended
	Dec. 31, 2014
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,
		2014			2013			2012
	Net loss	$	(23,342	)	$	(17,143	)	$	(22,101	)
	Accretion of preferred stock issuance costs to redemption value		—			—			(73	)
	Net loss attributable to common stockholders — basic and diluted	$	(23,342	)	$	(17,143	)	$	(22,174	)
	Weighted-average number of common shares — basic and diluted		14,548,516			684,330			609,344
	Net loss per share attributable to common stockholders — basic and diluted	$	(1.60	)	$	(25.05	)	$	(36.39	)
Potentially Dilutive Securities Excluded from Computation of Diluted Weighted-Average Shares Outstanding	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,
		2014			2013			2012
	Options to purchase common stock		2,126,176			1,062,694			1,046,178
	Warrants to purchase redeemable convertible preferred stock		—			128,663			128,663
	Warrants to purchase common stock		128,663			—			—
	Redeemable convertible preferred stock		—			6,826,004			6,992,694
	Convertible notes payable		—			754,785			—

Property_and_Equipment_Tables

Property and Equipment (Tables)	12 Months Ended
	Dec. 31, 2014
Property Plant And Equipment [Abstract]
Summary of Property and Equipment	Property and equipment consist of the following (in thousands):
		As of December 31,
		2014			2013
	Laboratory equipment	$	1,163		$	1,246
	Computer equipment		260			183
	Office furniture and equipment		292			257
	Leasehold improvements		117			91
			1,832			1,777
	Less accumulated depreciation and amortization		(1,490	)		(1,532	)
	Property and equipment, net	$	342		$	245

Accrued_Expenses_Tables

Accrued Expenses (Tables)	12 Months Ended
	Dec. 31, 2014
Payables And Accruals [Abstract]
Schedule of Accrued Expenses	Accrued expenses consist of the following (in thousands):
		As of December 31,
		2014		2013
	Accrued expenses	$	663	$	379
	Accrued clinical trial costs		848		610
	Accrued contract manufacturing expenses		580		433
	Accrued compensation and benefits		983		618
	Accrued interest		574		234
	Total accrued expenses	$	3,648	$	2,274

Loan_Agreements_Tables

Loan Agreements (Tables)	12 Months Ended
	Dec. 31, 2014
Debt Instrument [Line Items]
Summary of Minimum Future Principal Payments	The minimum future principal payments are as follows (in thousands):
	Year Ending December 31,
	2015	$	3,321
	Unamortized discount relating to warrants		(197	)
	Total		3,124
	Less current portion		(3,124	)
	Long-term portion	$	-
Fair Value of Preferred 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:
		31-Dec-13
	Expected life	4-8 years
	Risk-free interest rate		2.9	%
	Expected volatility	64%-84%
	Expected dividend rate	—%
Loan and Security Agreement with Bank [Member]
Debt Instrument [Line Items]
Fair Value of Preferred Stock Warrants Calculated using Black-Scholes Assumptions	The following table shows the Black-Scholes assumptions used to value the preferred stock warrants in connection with the loan and security agreement on the respective dates:
		Series D Preferred Stock Warrants
		December 2011			Mar-12			Aug-12
	Contractual life	10 years			9.69 years			9.29 years
	Volatility rate		80	%		80	%		80	%
	Risk-free interest rate		1.98	%		2.17	%		1.68	%
	Expected dividends		—			—			—

Redeemable_Convertible_Preferr1

Redeemable Convertible Preferred Stock (Tables)	12 Months Ended
	Dec. 31, 2014
Temporary Equity Disclosure [Abstract]
Schedule of Preferred Stock	As of December 31, 2013, preferred stock consisted of the following (in thousands, except share data):
		Preferred		Issuance Date	Preferred Shares		Redemption		Carrying Value
		Shares			Issued and		Value /Liquidation
		Authorized			Outstanding		Preference
	Seed		2,500,000	Dec-06		2,500,000	$	2,000	$	2,000
	Series A		9,307,692	May-07		9,307,692		12,100		12,100
	Series B		4,077,500	Dec-07		3,562,500		7,125		7,125
	Series B-1		5,000,000	Jul-09		4,842,500		9,685		9,685
	Series C		33,310,787	November 2010 and June 2011		31,836,392		23,559		23,094
	Series D		34,698,793	December 2011 and November 2012		33,158,272		27,521		27,521
			88,894,772			85,207,356	$	81,990	$	81,525

Stockholders_Equity_Deficit_Ta

Stockholders' Equity (Deficit) (Tables)	12 Months Ended
	Dec. 31, 2014
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, 2014 and 2013:
		As of December 31,
		2014		2013
	Redeemable convertible preferred stock		—		6,954,691
	Warrants to purchase common stock		128,663		—
	Common stock options		3,561,104		1,201,770
	Total		3,689,767		8,156,461

Stock_Option_Plans_Tables

Stock Option Plans (Tables)	12 Months Ended
	Dec. 31, 2014
Summary of Stock Option Activity for Employee and Nonemployee Awards under 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, 2014 is presented below:
		Number of			Weighted-		Weighted-		Aggregate
		Shares			Average		Average		Intrinsic
					Exercise		Remaining		Value
					Price		Contractual
							Life (Years)
	Outstanding — January 1, 2014		1,062,694		$	3.98		7.2	$	7,028
	Granted		1,138,170			5.99
	Exercised		(41,566	)		3.36
	Forfeited		(33,122	)		4.85
	Outstanding — December 31, 2014		2,126,176		$	4.97		6.7	$	2,701
	Options expected to vest — December 31, 2014		859,690		$	5.46		9.2	$	1,105
	Options exercisable — December 31, 2014		786,623		$	4.41		3.9	$	1,541
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,
		2014			2013		2012
	Research and development	$	317		$	284	$	187
	General and administrative		568			338		342
	Total	$	885		$	622	$	529
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, 2014, 2013 and 2012 are as follows:
		December 31,
		2014		2013	2012
	Expected life	6 years		6 years	6 years
	Risk-free interest rate	1.71%-2.00%		1.09%-1.92%	0.83%-1.12%
	Expected volatility	54%-60%		59%-79%	77%-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, 2014, 2013 and 2012 were as follows:
		December 31,
		2014		2013	2012
	Expected life	8 years		7 years	6 years
	Risk-free interest rate	1.86%-2.53%		1.11%-2.86%	0.99%-2.05%
	Expected volatility	56%-62%		56%-79%	76%-79%
	Expected dividend rate	—%		—%	—%

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2014
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, 2014 and 2013, is as follows (in thousands):
					Fair Value Measurements Using
		Carrying			Quoted Prices in			Significant			Significant
					Active Markets			Other			Unobservable
					for Identical			Observable			Inputs
					Assets			Inputs
		Value			(Level 1)			(Level 2)			(Level 3)
	31-Dec-14
	Money market funds	$	50,541		$	—		$	50,541		$	—
	31-Dec-13
	Money market funds	$	5,233		$	—		$	5,233		$	—
	Preferred stock warrant liability		928			—			—			928
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, 2012	$	7		$	500		$	623		$	1,130
	Decrease in fair value recorded in other income		(3	)		(114	)		(85	)		(202	)
	Balance — December 31, 2013		4			386			538			928
	Fair value reclassified to additional paid-in capital in connection		(4	)		(386	)		(538	)		(928	)
	with the IPO on April 15, 2014
	Balance — December 31, 2014	$	-		$	-		$	-		$	-
Fair Value of Preferred 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:
		31-Dec-13
	Expected life	4-8 years
	Risk-free interest rate		2.9	%
	Expected volatility	64%-84%
	Expected dividend rate	—%

Income_Taxes_Tables

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2014
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:
		2014			2013
	Net operating loss carryforwards	$	29,442		$	25,696
	Research and development credit carryforwards		1,715			1,525
	Capitalized costs		3,503			3,067
	Capitalized research and development costs		9,938			6,992
	Other		422			220
	Total deferred tax assets		45,020			37,500
	Valuation allowance		(45,020	)		(37,500	)
	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,
		2014			2013
	Federal income tax expense at statutory rate		34	%		34	%
	State income tax, net of federal benefit		4.5	%		5	%
	Permanent differences		(3.7	%)		0.2	%
	Research and development credit		0.8	%		1.4	%
	Stock compensation		(0.9	%)		(1.1	%)
	Expiration of state net operating loss		(1.7	%)		(4.2	%)
	Other		(0.8	%)		0.2	%
	Change in valuation allowance		(32.2	%)		(35.5	%)
	Effective income tax rate		0	%		0	%

Commitments_Tables

Commitments (Tables)	12 Months Ended
	Dec. 31, 2014
Commitments And Contingencies Disclosure [Abstract]
Summary of Future Minimum Lease Payments under Non-cancelable Operating Leases	Future minimum lease payments, including the three-year extension, under the non-cancelable operating lease are as follows (in thousands):
		Operating
	Years Ending December 31,	Leases
	2015		954
	2016		160
	Total	$	1,114

Quarterly_Financial_Data_Unaud1

Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2014
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, 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
		Year Ended December 31, 2013
		First Quarter			Second Quarter			Third Quarter			Fourth Quarter
	Revenue	$	—		$	—		$	—		$	6
	Operating expenses:
	Research and development		3,479			3,195			1,586			1,440
	General and administrative		1,972			1,392			1,227			1,575
	Total operating expenses		5,451			4,587			2,813			3,015
	Other income (expense):
	Interest income		1			—			—			1
	Interest expense		(353	)		(326	)		(378	)		(430	)
	Loss on extinguishment of debt		—			—			—			—
	Decrease in value of preferred stock warrant liability		231			20			(7	)		(42	)
	Total other income (expense) — net		(121	)		(306	)		(385	)		(471	)
	Net loss attributable to common stockholders	$	(5,572	)	$	(4,893	)	$	(3,198	)	$	(3,480	)
	Net loss per share attributable to common stockholders:
	Basic and diluted	$	(9.09	)	$	(7.96	)	$	(4.40	)	$	(4.45	)
	Weighted-average common shares outstanding:
	Basic and diluted		612,836			614,662			726,987			782,335

Nature_of_Business_and_Operati1

Nature of Business and Operations - Additional Information (Detail) (USD $)	1 Months Ended	12 Months Ended	0 Months Ended
In Thousands, except Share data, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2014	7-May-14	Apr. 15, 2014	Dec. 31, 2013	Apr. 30, 2014
Nature Of Business And Operations [Line Items]
Date of Company's incorporation		28-Nov-05
Accumulated deficit		$121,781			$98,439
Proceeds from initial public offering, net		59,862
Reverse Stock Split, Conversion Ratio	14.5074
IPO [Member]
Nature Of Business And Operations [Line Items]
Common stock issuance date		15-Apr-14
Issuance of Common Stock from initial public offering, shares			1,069,715	8,500,000
Issuance/sale of stock, price per share			$7	$7
Proceeds from initial public offering, net			$59,900
Reverse stock split of common stock		The Company’s board of directors and stockholders approved a 1-for-14.5074 reverse stock split of the Company’s common stock effective March 31, 2014.
Convertible preferred stock, shares issued upon conversion				9,728,237		6,826,004
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 [Member]
Nature Of Business And Operations [Line Items]
Conversion of preferred warrants to common warrants.				1,857,226
IPO [Member] | Common Stock [Member]
Nature Of Business And Operations [Line Items]
Issuance of Common Stock from initial public offering, shares		9,569,715
Conversion of preferred warrants to common warrants.				128,663

Significant_Accounting_Policie3

Significant Accounting Policies - Additional Information (Detail) (USD $)	3 Months Ended			12 Months Ended
	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
				Segment
Disclosure - Significant Accounting Policies - Additional Information (Detail) [Line Items]
Revenue	$33,000	$47,000	$6,000	$80,000	$6,000	$625,000
Number of operating segments				1
Restricted cash			117,000	117,000	117,000
Facility lease scheduled expiration period				2016-02
Sydney, NSW [Member]
Disclosure - Significant Accounting Policies - Additional Information (Detail) [Line Items]
Revenue				0
Long-lived assets				$0

Significant_Accounting_Policie4

Significant Accounting Policies - Schedule of Property and Equipment Estimated Useful Lives (Detail)	12 Months Ended
	Dec. 31, 2014
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_Attributabl2

Net Loss Per Share Attributable to Common Stockholders - Schedule of Basic and Diluted Net Loss Per Common Share (Detail) (USD $)	3 Months Ended								12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Earnings Per Share [Abstract]
Net loss									($23,342)	($17,143)	($22,101)
Accretion of preferred stock issuance costs to redemption value											-73
Net loss attributable to common stockholders	($7,467)	($5,558)	($7,403)	($2,914)	($3,480)	($3,198)	($4,893)	($5,572)	($23,342)	($17,143)	($22,174)
Weighted-average number of common shares — basic and diluted	20,125,009	20,124,574	16,883,716	786,986	782,335	726,987	614,662	612,836	14,548,516	684,330	609,344
Net loss per share attributable to common stockholders — basic and diluted	($0.37)	($0.28)	($0.44)	($3.70)	($4.45)	($4.40)	($7.96)	($9.09)	($1.60)	($25.05)	($36.39)

Net_Loss_Per_Share_Attributabl3

Net Loss Per Share Attributable to Common Stockholders - Potentially Dilutive Securities Excluded from Computation of Diluted Weighted-Average Shares Outstanding (Detail)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
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	6,992,694
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	2,126,176	1,062,694	1,046,178
Warrants to Purchase 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	128,663
Warrants 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	128,663
Convertible Notes Payable [Member]
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

Property and Equipment - Summary of Property and Equipment (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Property Plant And Equipment [Line Items]
Property and equipment, gross	$1,832	$1,777
Less accumulated depreciation and amortization	-1,490	-1,532
Property and equipment, net	342	245
Laboratory Equipment [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	1,163	1,246
Computer Equipment [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	260	183
Office Furniture and Equipment [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	292	257
Leasehold Improvements [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	$117	$91

Property_and_Equipment_Additio

Property and Equipment - Additional Information (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Property Plant And Equipment [Abstract]
Depreciation and amortization	$126	$197	$346

Accrued_Expenses_Schedule_of_A

Accrued Expenses - Schedule of Accrued Expenses (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Payables And Accruals [Abstract]
Accrued expenses	$663	$379
Accrued clinical trial costs	848	610
Accrued contract manufacturing expenses	580	433
Accrued compensation and benefits	983	618
Accrued interest	574	234
Total accrued expenses	$3,648	$2,274

Convertible_Notes_Payable_to_S1

Convertible Notes Payable to Shareholders - Additional Information (Detail) (USD $)	0 Months Ended	1 Months Ended	3 Months Ended	12 Months Ended	0 Months Ended
	Apr. 15, 2014	Apr. 30, 2014	Jun. 30, 2014	Dec. 31, 2014	Nov. 30, 2010	Mar. 31, 2014	Aug. 31, 2013	Sep. 30, 2010	31-May-10
Debt Instrument [Line Items]
Debt instrument, Original principal amount							$8,824,000
Debt instrument stated interest rate						7.00%	7.00%
Debt instrument percentage	77.50%
IPO closure date				4/15/14
Loss on extinguishment of debt		-2,493,000	-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%
Preferred stock shares became exercisable	60,532
Fair value of warrants					474,000
Expected volatility					80.00%
Expected life					7 years
Risk-free interest rate					1.85%
Dividend yield					$0
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					9,021,175
Debt instrument conversion price					$0.74
Percentage to determine the number of shares included in warrants					10.00%
Preferred stock shares became exercisable					878,370
Preferred stock per share					$0.74
Convertible Promissory Notes [Member] | Existing Investors [Member]
Debt Instrument [Line Items]
Debt instrument, Original principal amount						6,000,000
Convertible Promissory Notes [Member] | New Investor [Member]
Debt Instrument [Line Items]
Debt instrument, Original principal amount						2,500,000

Loan_Agreements_Additional_Inf

Loan Agreements - Additional Information (Detail) (USD $)	3 Months Ended					12 Months Ended			1 Months Ended					6 Months Ended
	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Sep. 30, 2008	Aug. 31, 2008	Aug. 31, 2012	Mar. 31, 2012	Dec. 31, 2011	Aug. 31, 2012	Aug. 31, 2013	Apr. 30, 2014
Debt Instrument [Line Items]
Proceeds from loans payable								$10,000,000
Debt instrument stated interest rate	7.00%														7.00%
Fair value of outstanding warrants		928,000					928,000
Fair value adjustment of warrant liability	-504,000	42,000	7,000	-20,000	-231,000	-504,000	-202,000	-39,000
Accrued interest		234,000				574,000	234,000
Noncurrent accrued interest		391,000					391,000
Loan and Security Agreement with Bank [Member]
Debt Instrument [Line Items]
Loan and security agreement, maximum borrowing capacity										1,500,000
Proceeds from loans payable									695,000
Loan and security agreement, borrowings repayment period									48 months
Debt instrument stated interest rate									8.75%
Loan and Security Agreement with Bank [Member] | Common Stock [Member]
Debt Instrument [Line Items]
Conversion of preferred warrants to common warrants.																1,695
Loan and Security Agreement with Bank [Member] | Series B Convertible Preferred Stock [Member]
Debt Instrument [Line Items]
Conversion of preferred warrants to common warrants.										15,000
Exercise price of warrant										$2
Warrant expiration period										10 years
Fair value of outstanding warrants										25,000
Expected volatility										79.00%
Contractual life										10 years
Risk-free interest rate										3.89%
Expected dividends										0.00%
Loan and Security Agreement with Lighthouse Capital Partners VI, L.P. [Member]
Debt Instrument [Line Items]
Loan and security agreement, maximum borrowing capacity													10,000,000
Proceeds from loans 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						1-Dec-12
Line of credit facility, additional interest payment						600,000
Loan and Security Agreement with Lighthouse Capital Partners VI, L.P. [Member] | Common Stock [Member]
Debt Instrument [Line Items]
Conversion of preferred warrants to common warrants.																66,436
Loan and Security Agreement with Lighthouse Capital Partners VI, L.P. [Member] | Series D Convertible Preferred Stock [Member]
Debt Instrument [Line Items]
Conversion of preferred warrants to common warrants.													66,436
Exercise price of warrant													$12.04
Warrant expiration period													10 years
Fair value of outstanding warrants											$178,000	$182,000	$284,000	$178,000
Expected volatility											80.00%	80.00%	80.00%
Contractual life											9 years 3 months 15 days	9 years 8 months 9 days	10 years
Risk-free interest rate											1.68%	2.17%	1.98%
Warrant exercisable for preferred stock, shares		66,436				66,436	66,436						29,067
Warrant expiration date						2021-12

Loan_Agreements_Summary_of_Min

Loan Agreements - Summary of Minimum Future Principal Payments (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Debt Disclosure [Abstract]
2015	$3,321
Unamortized discount relating to warrants	-197
Total	3,124
Less current portion	-3,124	-3,134
Long-term portion		$3,124

Loan_Agreements_Fair_Value_of_

Loan Agreements - Fair Value of Preferred Stock Warrants Calculated using Black-Scholes Assumptions (Detail) (Loan and Security Agreement with Lighthouse Capital Partners VI, L.P. [Member], Series D Convertible Preferred Stock [Member])	1 Months Ended
	Aug. 31, 2012	Mar. 31, 2012	Dec. 31, 2011
Loan and Security Agreement with Lighthouse Capital Partners VI, L.P. [Member] | Series D Convertible Preferred Stock [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Contractual life	9 years 3 months 15 days	9 years 8 months 9 days	10 years
Expected volatility	80.00%	80.00%	80.00%
Risk-free interest rate	1.68%	2.17%	1.98%

Redeemable_Convertible_Preferr2

Redeemable Convertible Preferred Stock - Additional Information (Detail)	1 Months Ended
	Apr. 30, 2014
Temporary Equity Disclosure [Abstract]
Conversion of convertible preferred stock into common stock, shares	6,826,004

Redeemable_Convertible_Preferr3

Redeemable Convertible Preferred Stock - Schedule of Preferred Stock (Detail) (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2013
Temporary Equity [Line Items]
Preferred Shares Authorized	88,894,772
Preferred Shares Issued	85,207,356
Preferred Shares Outstanding	85,207,356
Redemption Value /Liquidation Preference	$81,990
Carrying Value	81,525
Seed Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred Shares Authorized	2,500,000
Issuance Date	2006-12
Preferred Shares Issued	2,500,000
Preferred Shares Outstanding	2,500,000
Redemption Value /Liquidation Preference	2,000
Carrying Value	2,000
Series A Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred Shares Authorized	9,307,692
Issuance Date	2007-05
Preferred Shares Issued	9,307,692
Preferred Shares Outstanding	9,307,692
Redemption Value /Liquidation Preference	12,100
Carrying Value	12,100
Series B Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred Shares Authorized	4,077,500
Issuance Date	2007-12
Preferred Shares Issued	3,562,500
Preferred Shares Outstanding	3,562,500
Redemption Value /Liquidation Preference	7,125
Carrying Value	7,125
Series B-1 Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred Shares Authorized	5,000,000
Issuance Date	2009-07
Preferred Shares Issued	4,842,500
Preferred Shares Outstanding	4,842,500
Redemption Value /Liquidation Preference	9,685
Carrying Value	9,685
Series C Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred Shares Authorized	33,310,787
Issuance Date	November 2010 and June 2011
Preferred Shares Issued	31,836,392
Preferred Shares Outstanding	31,836,392
Redemption Value /Liquidation Preference	23,559
Carrying Value	23,094
Series D Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred Shares Authorized	34,698,793
Issuance Date	December 2011 and November 2012
Preferred Shares Issued	33,158,272
Preferred Shares Outstanding	33,158,272
Redemption Value /Liquidation Preference	27,521
Carrying Value	$27,521

Stockholders_Equity_Deficit_Ad

Stockholders' Equity (Deficit) - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2014
Stockholders Equity Note [Abstract]
Issuance of common stock, shares	19,297,952

Stockholders_Equity_Deficit_Su

Stockholders' Equity (Deficit) - Summary of Number of Shares of Common Stock Reserved (Detail)	Dec. 31, 2014	Dec. 31, 2013
Class Of Stock [Line Items]
Reserved shares of common stock	3,689,767	8,156,461
Common stock options [Member]
Class Of Stock [Line Items]
Reserved shares of common stock	3,561,104	1,201,770
Redeemable Convertible Preferred Stock [Member]
Class Of Stock [Line Items]
Reserved shares of common stock		6,954,691
Warrants to Purchase Common Stock [Member]
Class Of Stock [Line Items]
Reserved shares of common stock	128,663

Stock_Option_Plans_Additional_

Stock Option Plans - Additional Information (Detail) (USD $)	12 Months Ended			0 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jan. 01, 2015	Jan. 31, 2014
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	$885,000	$622,000	$529,000
Number of Shares, Options expected to vest	859,690
Number of Shares, Granted	1,138,170
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	139,076
2014 Stock Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options vesting period	3 years
Shares available for future grant	1,434,928
Total intrinsic value of stock options exercised	161,000	15,000	0
Weighted-average per share grant date fair value of options granted	$3.33	$2.90	$2.61
Stock-based compensation expense	885,000	622,000	529,000
Unrecognized compensation cost related to unvested stock-based compensation arrangements	2,200,000
Weighted-average period of recognition of unrecognized compensation cost related to unvested stock-based compensation arrangements	3 years 7 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		53,489	56,053
2014 Stock Incentive Plan [Member] | Second Company Officer [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]
Stock-based compensation expense	$56,000	$85,000	$39,000
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
Shares issued under Employee Stock Purchase Plan during the period	0
2014 Employee Stock Purchase Plan [Member] | Subsequent Event
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Maximum shares of common stock provided under stock incentive plan				600,000
Percentage of common stock outstanding stock on first day of the year				1.00%

Stock_Option_Plans_Summary_of_

Stock Option Plans -Summary of Stock Option Activity for Employee and Nonemployee Awards under Plan (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Number of shares
Number of Shares, Outstanding	1,062,694
Number of Shares, Granted	1,138,170
Number of Shares, Exercised	-41,566
Number of Shares, Forfeited	-33,122
Number of Shares, Outstanding	2,126,176	1,062,694
Number of Shares, Options expected to vest	859,690
Number of Shares, Options exercisable	786,623
Weighted-Average Exercise Price
Weighted-Average Exercise Price, Outstanding	$3.98
Weighted-Average Exercise Price, Granted	$5.99
Weighted-Average Exercise Price, Exercised	$3.36
Weighted-Average Exercise Price, Forfeited	$4.85
Weighted-Average Exercise Price, Outstanding	$4.97	$3.98
Weighted-Average Exercise Price, Options expected to vest	$5.46
Weighted-Average Exercise Price, Options exercisable	$4.41
Weighted-Average Remaining Contractual Life (Years)
Weighted-Average Remaining Contractual Life (Years)	6 years 8 months 12 days	7 years 2 months 12 days
Weighted-Average Remaining Contractual Life (Years), Options expected to vest - December 31, 2014	9 years 2 months 12 days
Weighted-Average Remaining Contractual Life (Years), Options exercisable - December 31, 2014	3 years 10 months 24 days
Aggregate Intrinsic Value
Aggregate Intrinsic Value, Outstanding	$2,701	$7,028
Aggregate Intrinsic Value, Options expected to vest	1,105
Aggregate Intrinsic Value, Options exercisable	$1,541

Stock_Option_Plans_Schedule_of

Stock Option Plans - Schedule of Stock-based Compensation Expense (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$885	$622	$529
Research and Development [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	317	284	187
General and Administrative [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$568	$338	$342

Stock_Option_Plans_Summary_of_1

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, 2014	Dec. 31, 2013	Dec. 31, 2012
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected life	6 years	6 years	6 years
Risk-free interest rate, minimum	1.71%	1.09%	0.83%
Risk-free interest rate, maximum	2.00%	1.92%	1.12%
Expected volatility, minimum	54.00%	59.00%	77.00%
Expected volatility, maximum	60.00%	79.00%	79.00%
Non Employee Awards [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected life	8 years	7 years	6 years
Risk-free interest rate, minimum	1.86%	1.11%	0.99%
Risk-free interest rate, maximum	2.53%	2.86%	2.05%
Expected volatility, minimum	56.00%	56.00%	76.00%
Expected volatility, maximum	62.00%	79.00%	79.00%

Fair_Value_Measurements_Additi

Fair Value Measurements - Additional Information (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Fair Value Disclosures [Abstract]
Money market fund	$50,541	$5,233

Fair_Value_Measurements_Summar

Fair Value Measurements - Summary of Financial Assets and Liabilities Measured on Recurring Basis at Fair Value (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market fund	$50,541	$5,233
Preferred stock warrant liability		928
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market fund	50,541	5,233
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Preferred stock warrant liability		$928

Fair_Value_Measurements_Reconc

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], USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Preferred stock warrant liability, Beginning balance	$928	$1,130
Decrease in fair value recorded in other income		-202
Fair value reclassified to additional paid-in capital in connection with the IPO on April 15, 2014	-928
Preferred stock warrant liability, Ending Balance		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	7
Decrease in fair value recorded in other income		-3
Fair value reclassified to additional paid-in capital in connection with the IPO on April 15, 2014	-4
Preferred stock warrant liability, Ending Balance		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	500
Decrease in fair value recorded in other income		-114
Fair value reclassified to additional paid-in capital in connection with the IPO on April 15, 2014	-386
Preferred stock warrant liability, Ending Balance		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	623
Decrease in fair value recorded in other income		-85
Fair value reclassified to additional paid-in capital in connection with the IPO on April 15, 2014	-538
Preferred stock warrant liability, Ending Balance		$538

Fair_Value_Measurements_Fair_V

Fair Value Measurements - Fair Value of Preferred Stock Warrant Liability Calculated by Black-Scholes Option Pricing Model (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_Compo

Income Taxes - Significant Components of Company's Deferred Taxes (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Net operating loss carryforwards	$29,442	$25,696
Research and development credit carryforwards	1,715	1,525
Capitalized costs	3,503	3,067
Capitalized research and development costs	9,938	6,992
Other	422	220
Total deferred tax assets	45,020	37,500
Valuation allowance	-45,020	-37,500
Net deferred tax assets	$0	$0

Income_Taxes_Additional_Inform

Income Taxes - Additional Information (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Operating Loss Carryforwards [Line Items]
Increase (decrease) in valuation allowance	$7.60	$7.10
Net operating loss carryforwards expiration year	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
Federal [Member] | Research [Member]
Operating Loss Carryforwards [Line Items]
Research and development credit carryforwards	1.2
Research and development tax credit carryforwards expiration year	2034
State [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	58.1
State [Member] | Research [Member]
Operating Loss Carryforwards [Line Items]
Research and development credit carryforwards	$0.80
Research and development tax credit carryforwards expiration year	2029

Income_Taxes_Reconciliation_of

Income Taxes - Reconciliation of Income Tax Expense Computed at Statutory Federal Income Tax Rate to Income Taxes (Detail)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Federal income tax expense at statutory rate	34.00%	34.00%
State income tax, net of federal benefit	4.50%	5.00%
Permanent differences	-3.70%	0.20%
Research and development credit	0.80%	1.40%
Stock compensation	-0.90%	-1.10%
Expiration of state net operating loss	-1.70%	-4.20%
Other	-0.80%	0.20%
Change in valuation allowance	-32.20%	-35.50%
Effective income tax rate	0.00%	0.00%

Commitments_Additional_Informa

Commitments - Additional Information (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating Leased Assets [Line Items]
Noncancelable operating lease expire date	28-Feb-13
Noncancelable operating leases renewal option period	3 years
Deferred liability related to facility lease	$41	$12
Lease amendment, commencement Date	7/15/14
Noncancelable operating lease rent expenses	$766	$598	$517
Extended Lease
Operating Leased Assets [Line Items]
Noncancelable operating lease expire date	28-Feb-16

Commitments_Summary_of_Future_

Commitments - Summary of Future Minimum Lease Payments under Non-cancelable Operating Leases (Detail) (USD $)	Dec. 31, 2014
In Thousands, unless otherwise specified
Commitments And Contingencies Disclosure [Abstract]
2015	$954
2016	160
Total	$1,114

Licensing_Agreements_Additiona

Licensing Agreements - Additional Information (Detail) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Research And Development Arrangement Contract To Perform For Others [Line Items]
Research and development	$4,701,000	$2,928,000	$2,648,000	$1,495,000	$1,440,000	$1,586,000	$3,195,000	$3,479,000	$11,772,000	$9,700,000	$15,807,000
Calando Pharmaceuticals, Inc. [Member]
Research And Development Arrangement Contract To Perform For Others [Line Items]
Bankruptcy proceedings, court where petition was filed									District of Delaware
Bankruptcy petition date filed									3-Mar-15
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.
MIT License Agreement [Member]
Research And Development Arrangement Contract To Perform For Others [Line Items]
Research and development									10,000	10,000	10,000
Calando Product License Agreement [Member] | Upon achievement of specified regulatory and commercial milestones [Member]
Research And Development Arrangement Contract To Perform For Others [Line Items]
Milestone payment									32,800,000
Calando Platform License Agreement [Member] | CRLX301 [Member]
Research And Development Arrangement Contract To Perform For Others [Line Items]
Research and development									250,000
Calando Platform License Agreement [Member] | Upon achievement of specified regulatory and commercial milestones [Member]
Research And Development Arrangement Contract To Perform For Others [Line Items]
Milestone payment									17,800,000
Calando Platform License Agreement [Member] | Upon initiation of phase one clinical trial [Member] | CRLX301 [Member]
Research And Development Arrangement Contract To Perform For Others [Line Items]
Milestone payment									250,000
SUNY License Agreement [Member]
Research And Development Arrangement Contract To Perform For Others [Line Items]
Research and development									$30,000	$25,000	$10,000

Retirement_Plans_Additional_In

Retirement Plans - Additional Information (Detail) (Safe Harbor Plan [Member], USD $)	0 Months Ended	12 Months Ended
In Thousands, unless otherwise specified	Jan. 01, 2010	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Safe Harbor Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, employer matching contribution, percent of match	4.00%
Defined contribution plan, employer matching contribution		$163	$145	$165

Related_Party_Transactions_Add

Related Party Transactions - Additional Information (Detail) (USD $)	0 Months Ended	12 Months Ended
	Apr. 01, 2014	Dec. 31, 2014	Dec. 31, 2013	Apr. 30, 2014	Apr. 15, 2014
Related Party Transaction [Line Items]
Fees recorded offsetting research and development expenses		$39,000
Proceeds from sale of equipment	30,000
IPO [Member]
Related Party Transaction [Line Items]
Convertible preferred stock, shares issued upon conversion				6,826,004	9,728,237
Affiliated Entity [Member]
Related Party Transaction [Line Items]
Fees recorded offsetting research and development expenses			$84,000

Revenue_Additional_Information

Revenue - Additional Information (Detail) (USD $)	3 Months Ended			12 Months Ended
	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Revenue Recognition Milestone Method [Line Items]
Revenue	$33,000	$47,000	$6,000	$80,000	$6,000	$625,000
Material Transfer Agreement [Member]
Revenue Recognition Milestone Method [Line Items]
Revenue				61,000	6,000	625,000
Material Transfer Agreement One [Member]
Revenue Recognition Milestone Method [Line Items]
Revenue				$19,000

Subsequent_Events_Additional_I

Subsequent Events - Additional Information (Detail) (USD $)	0 Months Ended	12 Months Ended
	Jan. 08, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Subsequent Event [Line Items]
Proceeds from Issuance or Sale of Equity	$30,000,000
Debt Instrument, 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 provides for interest-only payments on a monthly basis until December 31, 2015
Long-term debt, maturities, prepayment terms		Any such prepayment of the Term Loan is subject to a prepayment charge of (i) 3.0% if such prepayment occurs within twelve months of the Closing Date, (ii) 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 (iii) 1.0% thereafter
Additional interest rate accrue on default		5.00%
Interest rate of final payment on principal amount		6.70%
Purchase of common stock, shares		20,125,049	785,531
Proceeds from sale of common stock		140,000	35,000	3,000
Subsequent Event
Subsequent Event [Line Items]
Number of tranches	3
Subsequent Event | Maximum [Member]
Subsequent Event [Line Items]
Proceeds from Issuance or Sale of Equity	40,000,000
Subsequent Event | Minimum [Member]
Subsequent Event [Line Items]
Amount of term loan facility required to be drawn	3,000,000
Hercules Technology Growth Capital, Inc. [Member] | Subsequent Event
Subsequent Event [Line Items]
Loan and security agreement, maximum borrowing capacity	26,000,000
Common stock per share	$6.05
Conversion of preferred warrants to common warrants.	137,521
Class of additional warrant or right number of securities called by warrants or rights	34,380
Class of warrant or right, date from which warrants or rights exercisable	8-Jan-20
Purchase of common stock, shares	135,501
Purchase price of common share	$7.38
Proceeds from sale of common stock	1,000,000
Borrowings One [Member] | Subsequent Event
Subsequent Event [Line Items]
Loan and security agreement, maximum borrowing capacity	15,000,000
Borrowings Two [Member] | Subsequent Event
Subsequent Event [Line Items]
Loan and security agreement, maximum borrowing capacity	5,000,000
Borrowings Three [Member] | Subsequent Event
Subsequent Event [Line Items]
Loan and security agreement, maximum borrowing capacity	$6,000,000

Quarterly_Financial_Data_Unaud2

Quarterly Financial Data (Unaudited) - Schedule of Quarterly Financial Data (Detail) (USD $)	1 Months Ended	3 Months Ended								12 Months Ended
In Thousands, except Share data, unless otherwise specified	Apr. 30, 2014	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Quarterly Financial Information Disclosure [Abstract]
Revenue				$33	$47	$6				$80	$6	$625
Operating expenses:
Research and development		4,701	2,928	2,648	1,495	1,440	1,586	3,195	3,479	11,772	9,700	15,807
General and administrative		2,607	2,441	2,029	1,510	1,575	1,227	1,392	1,972	8,587	6,166	6,393
Total operating expenses		7,308	5,369	4,677	3,005	3,015	2,813	4,587	5,451	20,359	15,866	22,200
Other income (expense):
Interest income		4	2	2	1	1			1	9	2	2
Interest expense		-163	-191	-268	-461	-430	-378	-326	-353	-1,083	-1,487	-567
Loss on extinguishment of debt	-2,493			-2,493						-2,493
Decrease in value of preferred stock warrant liability					504	-42	-7	20	231	504	202	39
Total other income (expense) — net		-159	-189	-2,759	44	-471	-385	-306	-121	-3,063	-1,283	-526
Net loss attributable to common stockholders		($7,467)	($5,558)	($7,403)	($2,914)	($3,480)	($3,198)	($4,893)	($5,572)	($23,342)	($17,143)	($22,174)
Net loss per share attributable to common stockholders:
Basic and diluted		($0.37)	($0.28)	($0.44)	($3.70)	($4.45)	($4.40)	($7.96)	($9.09)	($1.60)	($25.05)	($36.39)
Weighted-average common shares outstanding:
Basic and diluted		20,125,009	20,124,574	16,883,716	786,986	782,335	726,987	614,662	612,836	14,548,516	684,330	609,344