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Document and Entity Information - shares	9 Months Ended
Document and Entity Information - shares	Sep. 30, 2015	Nov. 10, 2015
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2015
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q3
Trading Symbol	CERU
Entity Registrant Name	CERULEAN PHARMA INC.
Entity Central Index Key	0001401914
Current Fiscal Year End Date	--12-31
Entity Filer Category	Smaller Reporting Company
Entity Common Stock, Shares Outstanding		27,346,780

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 77,631	$ 51,174
Accounts receivable, prepaid expenses, and other current assets	1,522	1,662
Total current assets	79,153	52,836
Property and equipment — Net	354	342
Other assets	610	215
Total	80,117	53,393
Current liabilities:
Current portion of loan payable	4,031	3,124
Accounts payable	2,158	1,255
Accrued expenses	4,402	3,648
Other liabilities	17	34
Total current liabilities	10,608	8,061
Long-term liabilities:
Loan payable — net of current portion	10,530
Non-current accrued interest	336
Other		7
Total long-term liabilities	10,866	7
Commitments
Stockholders’ equity:
Preferred stock, $0.01 par value; 5,000,000 shares authorized, no shares issued or outstanding
Common stock, $0.0001 par value; 120,000,000 shares authorized, 27,346,780 and 20,125,049 shares issued and outstanding at September 30, 2015 and December 31, 2014, respectively	3	2
Additional paid-in capital	209,307	167,104
Accumulated deficit	(150,667)	(121,781)
Total stockholders’ equity	58,643	45,325
Total	$ 80,117	$ 53,393

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2015	Dec. 31, 2014
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	120,000,000	120,000,000
Common stock, shares issued	27,346,780	20,125,049
Common stock, shares outstanding	27,346,780	20,125,049

Condensed Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Income Statement [Abstract]
Revenue				$ 80
Operating expenses:
Research and development	$ 7,092	$ 2,928	$ 18,791	7,071
General and administrative	2,954	2,441	8,352	5,980
Total operating expenses	10,046	5,369	27,143	13,051
Other income (expense):
Interest income	4	2	8	5
Interest expense	(509)	(191)	(1,751)	(920)
Loss on extinguishment of debt				(2,493)
Decrease in value of preferred stock warrant liability				504
Total other (expense) income — net	(505)	(189)	(1,743)	(2,904)
Net loss attributable to common stockholders	$ (10,551)	$ (5,558)	$ (28,886)	$ (15,875)
Net loss per share attributable to common stockholders:
Basic and diluted	$ (0.39)	$ (0.28)	$ (1.17)	$ (1.26)
Weighted-average common shares outstanding:
Basic and diluted	27,307,103	20,124,574	24,785,833	12,598,425

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Cash flows from operating activities:
Net loss	$ (28,886)	$ (15,875)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	1,731	628
Noncash rent expense	(24)	33
Change in carrying value of preferred stock warrant liability		(504)
Depreciation and amortization	129	93
Gain on disposal of property and equipment		(30)
Loss on extinguishment of debt		2,493
Noncash interest expense	1,020	329
Changes in operating assets and liabilities:
Accounts receivable, prepaid expenses and other current assets	185	(963)
Accounts payable	904	547
Accrued expenses	1,236	(204)
Net cash used in operating activities	(23,705)	(13,453)
Cash flows from investing activities:
Purchases of property and equipment	(141)	(116)
Proceeds from sale of property and equipment		40
Increase in restricted cash	(230)
Net cash used in provided by investing activities	(371)	(76)
Cash flows from financing activities:
Proceeds from sale of common stock	2,628	140
Proceeds from issuance of loans payable	15,000
Proceeds from issuance of convertible promissory notes		8,500
Payments on loans payable	(3,921)	(2,486)
Cash paid for debt issuance costs	(359)	(188)
Proceeds from public stock offering, net of issuance costs	37,185	59,861
Net cash provided by financing activities	50,533	65,827
Net increase in cash and cash equivalents	26,457	52,298
Cash and cash equivalents — Beginning of period	51,174	5,488
Cash and cash equivalents — End of period	77,631	57,786
Supplemental disclosures of noncash investing and financing activities:
Conversion of redeemable convertible preferred stock into common stock		81,525
Conversion of convertible notes and accrued interest into common stock, net		20,128
Reclassification of warrants to additional paid in capital		424
Supplemental cash flow information — Interest paid	$ 723	$ 326

Nature of Business and Operations

9 Months Ended

Sep. 30, 2015

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Nature of Business and Operations

1.	NATURE OF BUSINESS AND OPERATIONS

Nature of Business — Cerulean Pharma Inc. (the “Company”) was incorporated on November 28, 2005, as a Delaware corporation and is located in Cambridge, Massachusetts. The Company was formed to develop novel, nanotechnology-based therapeutics in the areas of oncology and other diseases.

Basis of Presentation — The consolidated financial statements include the accounts of the Company and its subsidiary, Cerulean Pharma Australia Pty Ltd, a wholly owned Australian-based proprietary limited company. All intercompany accounts and transactions have been eliminated. The consolidated interim financial statements of the Company included herein have been prepared, without audit, pursuant to the rules and regulations of the Securities and Exchange Commission (the “SEC”). Certain information and footnote disclosures normally included in financial statements prepared in accordance with accounting principles generally accepted in the United States of America have been condensed or omitted from this report, as is permitted by such rules and regulations. Accordingly, these condensed consolidated financial statements should be read in conjunction with the Company’s audited financial statements as of and for the year ended December 31, 2014, and notes thereto, included in the Company’s Annual Report on Form 10-K, which was filed with the Securities and Exchange Commission on March 19, 2015 (the “2015 10-K”).

The unaudited condensed consolidated financial statements have been prepared on the same basis as the audited consolidated financial statements. In the opinion of the Company’s management, the accompanying unaudited interim consolidated financial statements contain all adjustments that are necessary to present fairly the Company’s financial position as of September 30, 2015, the results of its operations for the three and nine months ended September 30, 2015 and 2014, and cash flows for the nine months ended September 30, 2015 and 2014. Such adjustments are of a normal and recurring nature. The results for the three and nine months ended September 30, 2015, are not indicative of the results for the year ending December 31, 2015, or for any future period.

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

On April 15, 2014, the Company completed the issuance and 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 the shares to the public resulted in net proceeds to the Company of $59.9 million after deducting underwriting discounts and commissions and offering expenses payable by the Company.

In connection with the closing of the IPO, all of the Company’s outstanding redeemable convertible preferred stock and convertible notes automatically converted into shares of common stock as of April 15, 2014, resulting in the issuance by the Company of an additional 9,728,237 shares of common stock. The significant increases in shares outstanding in April 2015 and April 2014 impacts the year-over-year comparability of the Company’s net loss per share calculations.

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.

Loan Agreements

9 Months Ended

Sep. 30, 2015

Debt Disclosure [Abstract]

Loan Agreements

6.	LOAN AGREEMENTS

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

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, 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 pay a final end of term charge to Hercules in the amount of 6.7% of the aggregate original principal amount advanced by Hercules. The amount of the end of term charge is being accrued over the loan term as interest expense.

In connection with the Hercules Loan Agreement, the Company issued to Hercules a warrant to purchase shares of the common stock of the Company at an exercise price of $6.05 per share. The warrant is 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 warrant is exercisable until January 8, 2020. The Company estimated the fair value of the warrant for shares exercisable on the issue date in January 2015 to be $659,000. The value of the warrant was recorded as a discount to the loan and will be amortized to interest expense using the effective interest method over the term of the loan. The fair value of the warrant was estimated on the date of issue for the exercisable shares at that date using the Black-Scholes option-pricing model. The following table shows the Black-Scholes assumptions used to value the warrant:

	January 8, 2015
Contractual life	5 years
Volatility rate		61	%
Risk-free interest rate		1.50	%
Expected dividends	—

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

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

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

Stock-Based Compensation

9 Months Ended

Sep. 30, 2015

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Compensation

7.	STOCK-BASED COMPENSATION

In March 2014, the Company’s board of directors adopted and its stockholders approved the 2014 Stock Incentive Plan (the “2014 Plan”) and the 2014 Employee Stock Purchase Plan (the “ESPP”), 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.

Stock Options

A summary of stock option activity for employee, director and nonemployee awards under all stock option plans during the nine months ended September 30, 2015 is presented below (Aggregate Intrinsic Value in thousands):

	Number of Shares			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Life (Years)		Aggregate Intrinsic Value
Outstanding — January 1, 2015		2,126,176		$	4.97		6.7	$	2,701
Granted		1,375,562			7.35
Exercised		(370,230	)		4.40
Forfeited		(609,736	)		5.83
Outstanding — September 30, 2015		2,521,772		$	6.21		8.7	$	49
Options expected to vest — September 30, 2015		1,631,896		$	6.52		9.2	$	-
Options exercisable — September 30, 2015		807,424		$	5.56		7.6	$	49

The weighted-average per share grant date fair value of options granted during the nine months ended September 30, 2015 and 2014 was $4.22 and $3.71, respectively.

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, and 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 Company has recorded stock-based compensation expense related to the issuance of stock option awards to employees of $773,000 and $272,000, for the three months ended September 30, 2015 and 2014, respectively, and $1.6 million and $591,000 for the nine months ended September 30, 2015 and 2014, respectively. The assumptions used in the Black-Scholes option-pricing model for stock options granted to employees and to directors in respect of board services during the three and nine months ended September 30, 2015 and 2014 are as follows:

	Three Months Ended September 30,		Nine Months Ended September 30,
	2015	2014	2015	2014
Expected life	6.0-6.1 years	6 years	5.4-6.1 years	6 years
Risk-free interest rate	1.65%-1.71%	1.86%-2.00%	1.45%-2.02%	1.83%-2.00%
Expected volatility	61%	57%-60%	61%-63%	57%-60%
Expected dividend rate	—%	—%	—%	—%

During the nine months ended September 30, 2015, the Company granted nonemployee stock options to consultants for the purchase of 192,000 shares of the Company’s common stock. The weighted-average exercise price and the weighted-average fair value of nonemployee stock options granted for the nine months ended September 30, 2015 was $5.28 per share and $2.33 per share, respectively. The fair value of the grants is being expensed over the vesting period of the options on a straight-line basis as the services are being provided. On September 4, 2015, nonemployee stock options to purchase 90,000 shares of the Company’s common stock were converted to employee stock options upon the appointment of the Company’s Chief Medical Officer who had been serving as a consultant to the Company until his appointment. The exercise price and the fair value of these stock options is $4.71 per share and $2.71 per share, respectively. The Company did not make any nonemployee stock option grants during the nine months ended September 30, 2014.

The Company recorded stock-based compensation expense related to nonemployee awards of $63,000 and $13,000 for the three months ended September 30, 2015 and 2014, respectively, and $135,000 and $37,000 for the nine months ended September 30, 2015 and 2014, respectively. The compensation expense related to 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 fair value for the three and nine months ended September 30, 2015 and 2014 were as follows:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2015			2014	2015			2014
Expected life	10 years			8 years	9.7-10 years			8 years
Risk-free interest rate		2.05	%	2.00%-2.53%	2.02%-2.12%			2.05%-2.53%
Expected volatility		59	%	56%-62%		60	%	56%-62%
Expected dividend rate	—%			—%	—%			—%

Employee Stock Purchase Plan

The ESPP permits eligible employees to enroll in a six-month offering period whereby participants may purchase shares of the Company’s common stock, through payroll deductions, at a price equal to 85% of the closing price of the common stock on the first day of the offering period or the last day of the offering period, whichever is lower. Purchase dates under the ESPP occur on or about June 30 and December 31 of each year. The first offering period under the ESPP opened on July 1, 2015. The stock-based compensation expense related to the ESPP for the three and nine months ended September 30, 2015 was $13,000. There was no stock-based compensation related to the ESPP recorded for the three and nine months ended September 30, 2014.

Fair Value Measurements

9 Months Ended

Sep. 30, 2015

Fair Value Disclosures [Abstract]

Fair Value Measurements

8.	FAIR VALUE MEASUREMENTS

The Company’s financial instruments consist of cash equivalents, accounts payable, accrued expenses, and debt obligations. 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 its fair value based on the short term nature of the debt and because the debt bears interest at the prevailing market rate for instruments with similar characteristics.

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 September 30, 2015 and December 31, 2014, is as follows (in thousands):

			Fair Value Measurements Using
	Carrying		Quoted Prices in Active Markets for Identical Assets		Significant Other Observable Inputs		Significant Unobservable Inputs
	Value		(Level 1)		(Level 2)		(Level 3)
September 30, 2015
Money market funds	$	77,323	$	—	$	77,323	$	—
December 31, 2014
Money market funds	$	50,541	$	—	$	50,541	$	—

The Company’s debt obligations are Level 2 measurements in the fair value hierarchy.

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.

No transfers between levels occurred during the periods presented.

- Definition

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

+ References + Details

Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2015

Summary of Stock Option Activity for Employee, Director and Nonemployee Awards

Stock Options

	Number of Shares			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Life (Years)		Aggregate Intrinsic Value
Outstanding — January 1, 2015		2,126,176		$	4.97		6.7	$	2,701
Granted		1,375,562			7.35
Exercised		(370,230	)		4.40
Forfeited		(609,736	)		5.83
Outstanding — September 30, 2015		2,521,772		$	6.21		8.7	$	49
Options expected to vest — September 30, 2015		1,631,896		$	6.52		9.2	$	-
Options exercisable — September 30, 2015		807,424		$	5.56		7.6	$	49

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

The assumptions used in the Black-Scholes option-pricing model for stock options granted to employees and to directors in respect of board services during the three and nine months ended September 30, 2015 and 2014 are as follows:

	Three Months Ended September 30,		Nine Months Ended September 30,
	2015	2014	2015	2014
Expected life	6.0-6.1 years	6 years	5.4-6.1 years	6 years
Risk-free interest rate	1.65%-1.71%	1.86%-2.00%	1.45%-2.02%	1.83%-2.00%
Expected volatility	61%	57%-60%	61%-63%	57%-60%
Expected dividend rate	—%	—%	—%	—%

Non Employee Awards [Member]

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

The Black-Scholes assumptions used to estimate fair value for the three and nine months ended September 30, 2015 and 2014 were as follows:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2015			2014	2015			2014
Expected life	10 years			8 years	9.7-10 years			8 years
Risk-free interest rate		2.05	%	2.00%-2.53%	2.02%-2.12%			2.05%-2.53%
Expected volatility		59	%	56%-62%		60	%	56%-62%
Expected dividend rate	—%			—%	—%			—%

Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2015

Fair Value Disclosures [Abstract]

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

A summary of the financial assets and liabilities that are measured on a recurring basis at fair value as of September 30, 2015 and December 31, 2014, is as follows (in thousands):

			Fair Value Measurements Using
	Carrying		Quoted Prices in Active Markets for Identical Assets		Significant Other Observable Inputs		Significant Unobservable Inputs
	Value		(Level 1)		(Level 2)		(Level 3)
September 30, 2015
Money market funds	$	77,323	$	—	$	77,323	$	—
December 31, 2014
Money market funds	$	50,541	$	—	$	50,541	$	—

Nature of Business and Operations - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands				9 Months Ended
	Apr. 10, 2015	May 07, 2014	Apr. 15, 2014	Sep. 30, 2015	Sep. 30, 2014
Nature Of Business And Operations [Line Items]
Date of Company's incorporation				Nov. 28, 2005
Common stock issuance date				Apr. 10, 2015
Issuance and sale of common stock, Shares	6,716,000
Common share offering price, per share	$ 6.00
Proceeds from sale of common stock	$ 37,200			$ 2,628	$ 140
Option Exercised by Underwriter [Member]
Nature Of Business And Operations [Line Items]
Issuance and sale of common stock, Shares	876,000
IPO [Member]
Nature Of Business And Operations [Line Items]
Common stock issuance date				Apr. 15, 2014
Issuance and sale of common stock, Shares		1,069,715	8,500,000
Issuance/sale of stock, price per share		$ 7.00	$ 7.00
Proceeds from initial public offering, net		$ 59,900
Preferred stock conversion basis				In connection with the closing of the IPO, all of the Company’s outstanding redeemable convertible preferred stock and convertible notes automatically converted into shares of common stock as of April 15, 2014
IPO [Member] \| Preferred Stock Warrants [Member]
Nature Of Business And Operations [Line Items]
Warrant to purchase stock, number of securities called by warrants or rights			1,857,226
IPO [Member] \| Common Stock Warrants [Member]
Nature Of Business And Operations [Line Items]
Number of automatically converted shares			128,663
IPO [Member] \| Common Stock [Member]
Nature Of Business And Operations [Line Items]
Number of automatically converted shares			9,728,237

Accrued Expenses - Schedule of Accrued Expenses (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Payables And Accruals [Abstract]
Accrued clinical trial costs	$ 1,706	$ 848
Accrued contract manufacturing expenses	465	580
Accrued compensation and benefits	1,582	983
Accrued interest	91	574
Other accrued expenses	558	663
Total accrued expenses	$ 4,402	$ 3,648

Loan Agreements - Additional Information (Detail)			1 Months Ended				6 Months Ended	9 Months Ended
Loan Agreements - Additional Information (Detail)	Apr. 10, 2015 USD ($) shares	Jan. 08, 2015 USD ($) Tranches $ / shares shares	Jan. 31, 2015 USD ($)	Aug. 31, 2012 USD ($)	Mar. 31, 2012 USD ($)	Dec. 31, 2011 USD ($) $ / shares shares	Aug. 31, 2012 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)	Apr. 30, 2014 shares
Debt Instrument [Line Items]
Common stock, shares issued \| shares	6,716,000
Proceeds from sale of common stock	$ 37,200,000							$ 2,628,000	$ 140,000
Proceeds from loan payable								15,000,000
Accrued interest								$ 91,000		$ 574,000
Hercules Loan Agreement [Member] \| Term Loan [Member]
Debt Instrument [Line Items]
Prior written notice period to prepay term loan								7 days
Loan and Security Agreement with Lighthouse Capital [Member]
Debt Instrument [Line Items]
Accrued interest										$ 574,000
Loan and Security Agreement with Lighthouse Capital [Member] \| Loans payable [Member]
Debt Instrument [Line Items]
Loan and security agreement, maximum borrowing capacity						$ 10,000,000
Proceeds from loan payable				$ 5,000,000	$ 5,000,000		$ 10,000,000
Loan and security agreement, borrowings repayment period						36 months
Debt instrument stated interest rate						8.25%
Loan and security agreement, borrowings repayment start date						Dec. 01, 2012
Line of credit facility, additional interest payment								$ 600,000
Repayments of notes payable			$ 3,600,000
Unamortized discount relating to warrants			200,000
Loan and Security Agreement with Lighthouse Capital [Member] \| Loans payable [Member] \| Series D Convertible Preferred Stock [Member]
Debt Instrument [Line Items]
Exercise price of warrant \| $ / shares						$ 12.04
Warrant expiration date						2021-12
Warrant expiration period						10 years
Loan and Security Agreement with Lighthouse Capital [Member] \| Loans payable [Member] \| Common Stock [Member]
Debt Instrument [Line Items]
Warrant to purchase stock, number of securities called by warrants or rights \| shares											66,436
Loan and Security Agreement with Lighthouse Capital [Member] \| Maximum [Member] \| Loans payable [Member] \| Series D Convertible Preferred Stock [Member]
Debt Instrument [Line Items]
Warrant to purchase stock, number of securities called by warrants or rights \| shares						66,436
Hercules Technology Growth Capital, Inc. [Member] \| Hercules Loan Agreement [Member] \| Stock Purchase Agreement [Member]
Debt Instrument [Line Items]
Common stock, shares issued \| shares		135,501
Issuance/sale of stock, price per share \| $ / shares		$ 7.38
Proceeds from sale of common stock		$ 1,000,000
Hercules Technology Growth Capital, Inc. [Member] \| Hercules Loan Agreement [Member] \| Term Loan [Member]
Debt Instrument [Line Items]
Loan and security agreement, maximum borrowing capacity		$ 26,000,000
Term loan facility, maturity date		Jul. 01, 2018
Term loan facility, interest rate terms								The Term Loan will mature on July 1, 2018. Each advance under the Term Loan accrues interest at a floating per annum rate equal to the greater of (i) 7.30% or (ii) the sum of 7.30% plus the prime rate minus 5.75%. The Term Loan provides for interest-only payments on a monthly basis until December 31, 2015.
Interest only period extension requirement, minimum net cash proceeds required from issuance and sale of equity securities		$ 30,000,000
Additional interest rate during an event of default		5.00%
Final payment as percentage of aggregate original principal amount		6.70%
Term loan facility, interest rate		7.30%
Class of warrant or right, date until which warrants exercisable		Jan. 08, 2020
Estimated fair value of warrant			$ 659,000
Hercules Technology Growth Capital, Inc. [Member] \| Hercules Loan Agreement [Member] \| Term Loan [Member] \| Common Stock [Member]
Debt Instrument [Line Items]
Exercise price of warrant \| $ / shares		$ 6.05
Warrant to purchase stock, number of securities called by warrants or rights \| shares		137,521
Hercules Technology Growth Capital, Inc. [Member] \| Hercules Loan Agreement [Member] \| Term Loan [Member] \| If Payment Occurs Within Twelve Months Of Closing Date [Member]
Debt Instrument [Line Items]
Debt prepayment charge		3.00%
Hercules Technology Growth Capital, Inc. [Member] \| Hercules Loan Agreement [Member] \| Term Loan [Member] \| If Payment Occurs After Twelve Months But on or Prior to Twenty Four Months Following Closing Date [Member]
Debt Instrument [Line Items]
Debt prepayment charge		2.00%
Hercules Technology Growth Capital, Inc. [Member] \| Hercules Loan Agreement [Member] \| Term Loan [Member] \| If Payment Occurs on or After Twenty Four Months Following Closing Date [Member[
Debt Instrument [Line Items]
Debt prepayment charge		1.00%
Hercules Technology Growth Capital, Inc. [Member] \| Hercules Loan Agreement [Member] \| Term Loan [Member] \| Prime Rate [Member]
Debt Instrument [Line Items]
Term loan facility, interest rate spread		5.75%
Hercules Technology Growth Capital, Inc. [Member] \| Hercules Loan Agreement [Member] \| Term Loan [Member] \| Borrowing One [Member]
Debt Instrument [Line Items]
Loan and security agreement, maximum borrowing capacity		$ 15,000,000
Hercules Technology Growth Capital, Inc. [Member] \| Hercules Loan Agreement [Member] \| Term Loan [Member] \| Up on Meeting Certain Clinical Milestone on or Prior to Dec. 15, 2015 [Member]
Debt Instrument [Line Items]
Loan and security agreement, maximum borrowing capacity		5,000,000
Hercules Technology Growth Capital, Inc. [Member] \| Hercules Loan Agreement [Member] \| Term Loan [Member] \| Up on Receipt of Net Cash Proceeds of at least $40 Million from Issuance of Equity Securities or Payment from Strategic Corporate Partnerships [Member]
Debt Instrument [Line Items]
Loan and security agreement, maximum borrowing capacity		6,000,000
Customary funding conditions minimum net cash proceeds required from issuance and sale of equity securities		$ 40,000,000
Warrant to purchase stock, number of securities called by warrants or rights \| shares		34,380
Hercules Technology Growth Capital, Inc. [Member] \| Hercules Loan Agreement [Member] \| Term Loan [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Number of tranches \| Tranches		3
Hercules Technology Growth Capital, Inc. [Member] \| Hercules Loan Agreement [Member] \| Term Loan [Member] \| Minimum [Member] \| Up on Receipt of Net Cash Proceeds of at least $40 Million from Issuance of Equity Securities or Payment from Strategic Corporate Partnerships [Member]
Debt Instrument [Line Items]
Amount of term loan facility required to be drawn		$ 3,000,000

Stock-Based Compensation - Summary of Stock Option Activity for Employee, Director and Nonemployee Awards (Detail) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Number of shares
Number of Shares, Outstanding	2,126,176
Number of Shares, Granted	1,375,562
Number of Shares, Exercised	(370,230)
Number of Shares, Forfeited	(609,736)
Number of Shares, Outstanding	2,521,772	2,126,176
Number of Shares, Options expected to vest	1,631,896
Number of Shares, Options exercisable	807,424
Weighted-Average Exercise Price
Weighted-Average Exercise Price, Outstanding	$ 4.97
Weighted-Average Exercise Price, Granted	7.35
Weighted-Average Exercise Price, Exercised	4.40
Weighted-Average Exercise Price, Forfeited	5.83
Weighted-Average Exercise Price, Outstanding	6.21	$ 4.97
Weighted-Average Exercise Price, Options expected to vest	6.52
Weighted-Average Exercise Price, Options exercisable	$ 5.56
Weighted-Average Remaining Contractual Life (Years)
Weighted-Average Remaining Contractual Life (Years)	8 years 8 months 12 days	6 years 8 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	7 years 7 months 6 days
Aggregate Intrinsic Value
Aggregate Intrinsic Value, Outstanding	$ 49	$ 2,701
Aggregate Intrinsic Value, Options expected to vest	0
Aggregate Intrinsic Value, Options exercisable	$ 49

Stock-Based Compensation - Additional Information (Detail) - USD ($)		3 Months Ended		9 Months Ended
	Sep. 04, 2015	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average per share grant date fair value of options granted				$ 4.22	$ 3.71
Number of Shares, Granted				1,375,562
Weighted-Average Exercise Price, Options exercisable		$ 5.56		$ 5.56
Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense		$ 13,000	$ 0	$ 13,000	$ 0
Purchase price as percentage of stock price on offering period				85.00%
Offering period				6 months
Employee Stock Options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense		773,000	272,000	$ 1,600,000	591,000
Non Employee Awards [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average per share grant date fair value of options granted	$ 2.71			$ 2.33
Stock-based compensation expense		$ 63,000	$ 13,000	$ 135,000	$ 37,000
Number of Shares, Granted	90,000			192,000	0
Weighted-Average Exercise Price, Options exercisable	$ 4.71	$ 5.28		$ 5.28

Stock-Based Compensation - Summary of Assumptions Used in Black-Scholes Option-Pricing Model for Stock Options Granted to Employees, Directors and Non Employees (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected life		6 years		6 years
Risk-free interest rate, minimum	1.65%	1.86%	1.45%	1.83%
Risk-free interest rate, maximum	1.71%	2.00%	2.02%	2.00%
Expected volatility	61.00%
Expected volatility, minimum		57.00%	61.00%	57.00%
Expected volatility, maximum		60.00%	63.00%	60.00%
Non Employee Awards [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected life	10 years	8 years		8 years
Risk-free interest rate, minimum		2.00%	2.02%	2.05%
Risk-free interest rate, maximum		2.53%	2.12%	2.53%
Expected volatility	59.00%		60.00%
Expected volatility, minimum		56.00%		56.00%
Expected volatility, maximum		62.00%		62.00%
Risk-free interest rate	2.05%
Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected life	6 years		5 years 4 months 24 days
Minimum [Member] \| Non Employee Awards [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected life			9 years 8 months 12 days
Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected life	6 years 1 month 6 days		6 years 1 month 6 days
Maximum [Member] \| Non Employee Awards [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected life			10 years

Significant Accounting Policies (Policies)	9 Months Ended
Significant Accounting Policies (Policies)	Sep. 30, 2015
Accounting Policies [Abstract]
Recent Accounting Pronouncements	Recent Accounting Pronouncements – In April 2015, the Financial Accounting Standards Board issued Accounting Standards Update 2015-03, “Interest – Imputation of Interest” (“ASU 2015-03”). To simplify presentation of debt issuance costs, ASU 2015-03 requires that debt issuance costs related to a recognized debt liability be presented in the balance sheet as a direct deduction from the carrying amount of that debt liability, consistent with debt discounts. ASU 2015-03 is effective for annual and interim reporting periods beginning January 1, 2016, and is not expected to have a material impact on the Company’s consolidated financial statements.

Net Loss Per Share Attributable to Common Stockholders - Potentially Dilutive Securities Excluded from Computation of Diluted Weighted-Average Shares Outstanding (Detail) - shares	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
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	2,521,772	1,798,264
Warrants [Member] \| Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted weighted-average shares outstanding	300,564	128,663

Convertible Notes Payable to Shareholders - Additional Information (Detail)	1 Months Ended	2 Months Ended	9 Months Ended
	Apr. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	Sep. 30, 2014 USD ($)
Debt Instrument [Line Items]
Loss on extinguishment of debt			$ (2,493,000)
Convertible Notes Payable [Member]
Debt Instrument [Line Items]
Debt instrument stated interest rate		7.00%
Debt instrument, Conversion Ratio		0.775
Loss on extinguishment of debt	$ (2,500,000)
Convertible Notes Payable [Member] \| Existing Investors [Member]
Debt Instrument [Line Items]
Debt instrument, Original principal amount		$ 6,000,000
Convertible Notes Payable [Member] \| New Investor [Member]
Debt Instrument [Line Items]
Debt instrument, Original principal amount		$ 2,500,000

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

Fair Value Measurements - Summary of Financial Assets and Liabilities Measured on Recurring Basis at Fair Value (Detail) - Fair Value, Measurements, Recurring [Member] - Money Market Funds [Member] - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Carrying Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	$ 77,323	$ 50,541
Fair Value Measurements [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	$ 77,323	$ 50,541