Document and Entity Information - shares	3 Months Ended
Document and Entity Information - shares	Mar. 31, 2016	Apr. 25, 2016
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2016
Document Fiscal Year Focus	2016
Document Fiscal Period Focus	Q1
Trading Symbol	CERU
Entity Registrant Name	CERULEAN PHARMA INC.
Entity Central Index Key	0001401914
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		27,363,965

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 60,515	$ 75,908
Accounts receivable, prepaid expenses, and other current assets	1,586	1,394
Total current assets	62,101	77,302
Property and equipment, net	693	576
Other assets	230	347
Total	63,024	78,225
Current liabilities:
Current portion of loan payable	7,832	7,652
Accounts payable	2,190	2,226
Accrued expenses	5,559	6,459
Total current liabilities	15,581	16,337
Long-term liabilities:
Loan payable, net of current portion	10,687	12,672
Other long-term liabilities	773	473
Total long-term liabilities	$ 11,460	$ 13,145
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, 27,363,965 and 27,346,780 shares issued and outstanding at March 31, 2016 and December 31, 2015, respectively	$ 3	$ 3
Additional paid-in capital	210,897	210,115
Accumulated deficit	(174,917)	(161,375)
Total stockholders’ equity	35,983	48,743
Total	$ 63,024	$ 78,225

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2016	Dec. 31, 2015
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	27,363,965	27,346,780
Common stock, shares outstanding	27,363,965	27,346,780

Condensed Consolidated Statements of Operations (unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Operating expenses:
Research and development	$ 9,770	$ 5,021
General and administrative	3,118	2,681
Total operating expenses	12,888	7,702
Other income (expense):
Interest income	16	3
Interest expense	(663)	(721)
Other expense	(7)	(8)
Total other expense, net	(654)	(726)
Net loss attributable to common stockholders	$ (13,542)	$ (8,428)
Net loss per share attributable to common stockholders:
Basic and diluted	$ (0.49)	$ (0.41)
Weighted-average common shares outstanding:
Basic and diluted	27,362,643	20,350,557

Condensed Consolidated Statements of Cash Flows (unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Cash flows from operating activities:
Net loss	$ (13,542)	$ (8,428)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	741	440
Noncash rent expense	124	(6)
Depreciation and amortization	61	41
Amortization of debt discount and deferred financing costs	127	515
Loss on disposal of property and equipment	4
Changes in operating assets and liabilities:
Accounts receivable, prepaid expenses and other current assets	(192)	(120)
Accounts payable	141	378
Accrued expenses	(724)	(761)
Net cash used in operating activities	(13,260)	(7,941)
Cash flows from investing activities:
Purchases of property and equipment	(359)	(29)
Decrease in restricted cash	117
Net cash used in investing activities	(242)	(29)
Cash flows from financing activities:
Proceeds from sale of common stock	41	2,411
Proceeds from issuance of loans payable		15,000
Payments on loans payable	(1,932)	(3,921)
Cash paid for debt issuance costs		(359)
Cash paid for deferred financing costs		(19)
Net cash (used in) provided by financing activities	(1,891)	13,112
Net increase in cash and cash equivalents	(15,393)	5,142
Cash and cash equivalents — Beginning of period	75,908	51,174
Cash and cash equivalents — End of period	60,515	56,316
Supplemental cash flow information — Interest paid	$ 372	$ 163

Nature of Business and Operations

3 Months Ended

Mar. 31, 2016

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Nature of Business and Operations

1.	NATURE OF BUSINESS AND OPERATIONS

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

Basis of Presentation — The condensed 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, 2015, and notes thereto, included in the Company’s Annual Report on Form 10-K, which was filed with the SEC on March 10, 2016 (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 condensed consolidated financial statements contain all adjustments that are necessary to present fairly the Company’s financial position as of March 31, 2016 and the results of its operations and cash flows for the three months ended March 31, 2016 and 2015. Such adjustments are of a normal and recurring nature. The results for the three months ended March 31, 2016, are not indicative of the results for the year ending December 31, 2016, or for any future period.

The Company has an accumulated deficit of $174.9 million at March 31, 2016. The Company has financed its operations primarily through private placements of its preferred stock, proceeds from borrowings, an initial public offering completed in 2014 and a follow-on offering completed in 2015. The Company has not completed development of any product candidate and has devoted substantially all of its financial resources and efforts to research and development, including preclinical and clinical development. Accordingly, the Company will continue to depend on its ability to raise capital through equity and debt issuances and/or through strategic partnerships. The Company expects to continue to incur significant expenses and increasing operating losses for at least several years. The Company believes that its cash and cash equivalents as of March 31, 2016, will be able to fund operating expenses, debt service and capital expenditure requirements for at least twelve months from the filing date of this Quarterly Report on Form 10-Q.

Significant Accounting Policies

3 Months Ended

Mar. 31, 2016

Accounting Policies [Abstract]

Significant Accounting Policies

2.	SIGNIFICANT ACCOUNTING POLICIES

There have been no material changes to the significant accounting policies previously disclosed in the 2015 10-K.

Recent Accounting Pronouncements – In March 2016, the Financial Accounting Standards Board (the “FASB”) issued Accounting Standards Update 2016-09, “Improvements to Employee Share-Based Payment Accounting” (“ASU 2016-09”). ASU 2016-09 is intended to simplify various aspects of how share-based payments are accounted for and presented in financial statements. The standard is effective prospectively for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2017, with early adoption permitted. The Company is currently evaluating the effect this standard will have on its consolidated financial statements and related disclosures.

In February 2016, the FASB issued Accounting Standards Update 2016-02, “Leases” (“ASU 2016-02”), which provides new accounting guidance on leases. ASU 2016-02 requires lessees to recognize leases on their balance sheets, and leaves lessor accounting largely unchanged. The amendments in ASU 2016-02 are effective for fiscal years beginning after December 15, 2018 and interim periods within those fiscal years. Early application is permitted for all entities. ASU 2016-02 requires a modified retrospective approach for all leases existing at, or entered into after, the date of initial application, with an option to elect to use certain transition relief. The Company is currently evaluating the impact of this new standard on its consolidated financial statements and related disclosures.

In August 2014, the FASB issued Accounting Standards Update 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.

Net Loss Per Share Attributable to Common Stockholders

3 Months Ended

Mar. 31, 2016

Earnings Per Share [Abstract]

Net Loss Per Share Attributable to Common Stockholders

3.	NET LOSS PER SHARE ATTRIBUTABLE TO COMMON STOCKHOLDERS

The Company computes diluted loss per common share after giving effect to the dilutive effect of stock options, warrants and shares of unvested restricted stock that are outstanding during the period, except where the inclusion of such securities would be antidilutive.

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

The following potentially dilutive securities that were outstanding prior to the use of the treasury stock method have been excluded from the computation of diluted weighted-average shares outstanding, because the inclusion of such securities would have an antidilutive impact due to the losses reported (in common stock equivalent shares):

	As of March 31,
	2016		2015
Options to purchase common stock		3,991,586		2,660,498
Warrants to purchase common stock		300,564		300,564

Accrued Expenses

3 Months Ended

Mar. 31, 2016

Payables And Accruals [Abstract]

Accrued Expenses

4.	ACCRUED EXPENSES

Accrued expenses consist of the following (in thousands):

	As of March 31, 2016		As of December 31, 2015
Accrued clinical trial costs	$	2,579	$	2,631
Accrued contract manufacturing expenses		1,404		945
Accrued compensation and benefits		749		1,864
Accrued interest		116		136
Other accrued expenses		711		883
Total accrued expenses	$	5,559	$	6,459

Loan Agreements

3 Months Ended

Mar. 31, 2016

Debt Disclosure [Abstract]

Loan Agreements

5.	LOAN AGREEMENTS

On January 8, 2015 (the “Closing Date”), the Company entered into a term loan facility of up to $26.0 million (the “Term Loan”) with Hercules Technology Growth Capital, Inc. (“Hercules”). The proceeds were used to repay the Company’s existing term loan facility with Lighthouse Capital Partners VI, L.P. (“Lighthouse Capital”) and for general corporate and working capital purposes. At March 31, 2016 and December 31, 2015, the Company had $19.1 million and $21.0 million, respectively, outstanding under the Term Loan.

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

The Term Loan will mature on July 1, 2018. Each advance under the Term Loan accrues interest at a floating per annum rate equal to the greater of (i) 7.30% or (ii) the sum of 7.30% plus the prime rate minus 5.75%. The Term Loan provided for interest-only payments on a monthly basis until December 31, 2015. Thereafter, payments are payable monthly in equal installments of principal and interest to fully amortize the outstanding principal over the remaining term of the loan, subject to recalculation upon a change in the prime rate. The Company may prepay the Term Loan in whole or in part upon seven business days’ prior written notice to Hercules. Any such prepayment of the Term Loan is subject to a prepayment charge of 2.0% if such prepayment occurs after twelve months following the Closing Date but on or prior to twenty-four months following the Closing Date, or 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 exercisable for 171,901 shares of common stock. The warrant is exercisable until January 8, 2020. The Company estimated the fair value of the warrant for shares exercisable on the issue date in January 2015 to be $824,000. The value of the warrant was recorded as a discount to the loan 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. 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 Company’s initial public offering. 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

3 Months Ended

Mar. 31, 2016

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Compensation

6.	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 in April 2014. 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 three months ended March 31, 2016 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, 2016		3,454,926		$	5.39		8.9	$	—
Granted		547,070			2.98
Exercised		—			—
Forfeited		(10,410	)		4.88
Outstanding — March 31, 2016		3,991,586		$	5.06		8.8	$	19
Options expected to vest — March 31, 2016		2,695,996		$	4.79		9.3	$	18
Options exercisable — March 31, 2016		1,159,945		$	5.72		7.7	$	—

The weighted-average per share grant date fair value of options granted during the three months ended March 31, 2016 and 2015 was $1.70 and $5.07, 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 $691,000 and $420,000 for the three months ended March 31, 2016 and 2015, 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 months ended March 31, 2016 and 2015 are as follows:

	Three Months Ended March 31,
	2016	2015
Expected life	5.9-6.1 years	6 years
Risk-free interest rate	1.31%-1.89%	1.45%-1.69%
Expected volatility	61%	61%-63%
Expected dividend rate	—%	—%

The Company recorded stock-based compensation expense related to nonemployee awards of $38,000 and $20,000 for the three months ended March 31, 2016 and 2015, 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 months ended March 31, 2016 and 2015 were as follows:

	Three Months Ended March 31,
	2016	2015
Expected life	6.9-9.7 years	8 years
Risk-free interest rate	1.7%-2.0%	1.86%
Expected volatility	60%-61%	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. During the three months ended March 31, 2016, 17,185 shares of common stock were purchased under the ESPP at a price of $2.38 per share. The stock-based compensation expense related to the ESPP for the three months ended March 31, 2016 was $12,000. There was no stock-based compensation related to the ESPP recorded for the three months ended March 31, 2015.

Fair Value Measurements

3 Months Ended

Mar. 31, 2016

Fair Value Disclosures [Abstract]

Fair Value Measurements

7.	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 March 31, 2016 and December 31, 2015, 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)
March 31, 2016
Money market funds	$	59,341	$	—	$	59,341	$	—
December 31, 2015
Money market funds	$	75,325	$	—	$	75,325	$	—

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

Significant Accounting Policies (Policies)	3 Months Ended
Significant Accounting Policies (Policies)	Mar. 31, 2016
Accounting Policies [Abstract]
Recent Accounting Pronouncements	Recent Accounting Pronouncements – In March 2016, the Financial Accounting Standards Board (the “FASB”) issued Accounting Standards Update 2016-09, “Improvements to Employee Share-Based Payment Accounting” (“ASU 2016-09”). ASU 2016-09 is intended to simplify various aspects of how share-based payments are accounted for and presented in financial statements. The standard is effective prospectively for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2017, with early adoption permitted. The Company is currently evaluating the effect this standard will have on its consolidated financial statements and related disclosures. In February 2016, the FASB issued Accounting Standards Update 2016-02, “Leases” (“ASU 2016-02”), which provides new accounting guidance on leases. ASU 2016-02 requires lessees to recognize leases on their balance sheets, and leaves lessor accounting largely unchanged. The amendments in ASU 2016-02 are effective for fiscal years beginning after December 15, 2018 and interim periods within those fiscal years. Early application is permitted for all entities. ASU 2016-02 requires a modified retrospective approach for all leases existing at, or entered into after, the date of initial application, with an option to elect to use certain transition relief. The Company is currently evaluating the impact of this new standard on its consolidated financial statements and related disclosures. In August 2014, the FASB issued Accounting Standards Update 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.

Net Loss Per Share Attributable to Common Stockholders (Tables)

3 Months Ended

Mar. 31, 2016

Earnings Per Share [Abstract]

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

	As of March 31,
	2016		2015
Options to purchase common stock		3,991,586		2,660,498
Warrants to purchase common stock		300,564		300,564

Accrued Expenses (Tables)

3 Months Ended

Mar. 31, 2016

Payables And Accruals [Abstract]

Schedule of Accrued Expenses

Accrued expenses consist of the following (in thousands):

	As of March 31, 2016		As of December 31, 2015
Accrued clinical trial costs	$	2,579	$	2,631
Accrued contract manufacturing expenses		1,404		945
Accrued compensation and benefits		749		1,864
Accrued interest		116		136
Other accrued expenses		711		883
Total accrued expenses	$	5,559	$	6,459

Loan Agreements (Tables)

3 Months Ended

Mar. 31, 2016

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

Debt Instrument [Line Items]

Fair Value of Stock Warrants Calculated using Black-Scholes Assumptions

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

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

Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2016

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, 2016		3,454,926		$	5.39		8.9	$	—
Granted		547,070			2.98
Exercised		—			—
Forfeited		(10,410	)		4.88
Outstanding — March 31, 2016		3,991,586		$	5.06		8.8	$	19
Options expected to vest — March 31, 2016		2,695,996		$	4.79		9.3	$	18
Options exercisable — March 31, 2016		1,159,945		$	5.72		7.7	$	—

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 months ended March 31, 2016 and 2015 are as follows:

	Three Months Ended March 31,
	2016	2015
Expected life	5.9-6.1 years	6 years
Risk-free interest rate	1.31%-1.89%	1.45%-1.69%
Expected volatility	61%	61%-63%
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 months ended March 31, 2016 and 2015 were as follows:

	Three Months Ended March 31,
	2016	2015
Expected life	6.9-9.7 years	8 years
Risk-free interest rate	1.7%-2.0%	1.86%
Expected volatility	60%-61%	62%
Expected dividend rate	—%	—%

Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2016

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 March 31, 2016 and December 31, 2015, 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)
March 31, 2016
Money market funds	$	59,341	$	—	$	59,341	$	—
December 31, 2015
Money market funds	$	75,325	$	—	$	75,325	$	—

Nature of Business and Operations - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Date of Company's incorporation	Nov. 28, 2005
Accumulated deficit	$ 174,917	$ 161,375

Net Loss Per Share Attributable to Common Stockholders - Potentially Dilutive Securities Excluded from Computation of Diluted Weighted-Average Shares Outstanding (Detail) - shares	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Options to Purchase Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted weighted-average shares outstanding	3,991,586	2,660,498
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	300,564

Accrued Expenses - Schedule of Accrued Expenses (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Payables And Accruals [Abstract]
Accrued clinical trial costs	$ 2,579	$ 2,631
Accrued contract manufacturing expenses	1,404	945
Accrued compensation and benefits	749	1,864
Accrued interest	116	136
Other accrued expenses	711	883
Total accrued expenses	$ 5,559	$ 6,459

Loan Agreements - Additional Information (Detail)		1 Months Ended				3 Months Ended		6 Months Ended
Loan Agreements - Additional Information (Detail)	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	Mar. 31, 2016 USD ($)	Mar. 31, 2015 USD ($)	Aug. 31, 2012 USD ($)	Dec. 31, 2015 USD ($)	Dec. 15, 2015 USD ($)	Nov. 24, 2015 USD ($)	Apr. 30, 2014 shares
Debt Instrument [Line Items]
Proceeds from sale of common stock						$ 41,000	$ 2,411,000
Proceeds from loan payable							$ 15,000,000
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] \| 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 on debt, 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]
Issuance of common stock, shares \| shares	135,501
Issuance/sale of stock, price per share \| $ / shares	$ 7.38
Proceeds from sale of common stock	$ 1,000,000
Hercules Technology Growth Capital, Inc. [Member] \| Hercules Loan Agreement [Member] \| Term Loan [Member]
Debt Instrument [Line Items]
Loan and security agreement, maximum borrowing capacity	$ 26,000,000
Amount outstanding under the Term Loan						$ 19,100,000			$ 21,000,000
Term loan facility, maturity date	Jul. 01, 2018
Term loan facility, interest rate terms						The Term Loan will mature on July 1, 2018. Each advance under the Term Loan accrues interest at a floating per annum rate equal to the greater of (i) 7.30% or (ii) the sum of 7.30% plus the prime rate minus 5.75%. The Term Loan provided for interest-only payments on a monthly basis until December 31, 2015.
Additional interest rate during an event of default	5.00%
Final payment as percentage of aggregate original principal amount	6.70%
Term loan facility, interest rate	7.30%
Debt prepayment charge, after twelve months	2.00%
Debt prepayment charge, after twenty-four months	1.00%
Class of warrant or right, date until which warrants exercisable	Jan. 08, 2020
Estimated fair value of warrant		$ 824,000
Hercules Technology Growth Capital, Inc. [Member] \| Hercules Loan Agreement [Member] \| Term Loan [Member] \| Common Stock [Member]
Debt Instrument [Line Items]
Exercise price of warrant \| $ / shares	$ 6.05
Warrant to purchase stock, number of securities called by warrants or rights \| shares	171,901
Hercules Technology Growth Capital, Inc. [Member] \| Hercules Loan Agreement [Member] \| Term Loan [Member] \| Prime Rate [Member]
Debt Instrument [Line Items]
Term loan facility, interest rate spread	5.75%
Hercules Technology Growth Capital, Inc. [Member] \| Hercules Loan Agreement [Member] \| Term Loan [Member] \| Borrowing One [Member]
Debt Instrument [Line Items]
Loan and security agreement, maximum borrowing capacity	$ 15,000,000
Hercules Technology Growth Capital, Inc. [Member] \| Hercules Loan Agreement [Member] \| Term Loan [Member] \| Second Tranche [Member]
Debt Instrument [Line Items]
Loan and security agreement, maximum borrowing capacity											$ 6,000,000
Hercules Technology Growth Capital, Inc. [Member] \| Hercules Loan Agreement [Member] \| Term Loan [Member] \| Up on Meeting Certain Clinical Milestone on or Prior to Dec. 15, 2015 [Member]
Debt Instrument [Line Items]
Loan and security agreement, maximum borrowing capacity										$ 5,000,000
Hercules Technology Growth Capital, Inc. [Member] \| Hercules Loan Agreement [Member] \| Term Loan [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Number of tranches \| Tranches	3

Loan Agreements - 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%

Stock-Based Compensation - Summary of Stock Option Activity for Employee, Director and Nonemployee Awards (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Number of shares
Number of Shares, Outstanding	3,454,926
Number of Shares, Granted	547,070
Number of Shares, Forfeited	(10,410)
Number of Shares, Outstanding	3,991,586	3,454,926
Number of Shares, Options expected to vest	2,695,996
Number of Shares, Options exercisable	1,159,945
Weighted-Average Exercise Price
Weighted-Average Exercise Price, Outstanding	$ 5.39
Weighted-Average Exercise Price, Granted	2.98
Weighted-Average Exercise Price, Forfeited	4.88
Weighted-Average Exercise Price, Outstanding	5.06	$ 5.39
Weighted-Average Exercise Price, Options expected to vest	4.79
Weighted-Average Exercise Price, Options exercisable	$ 5.72
Weighted-Average Remaining Contractual Life (Years)
Weighted-Average Remaining Contractual Life (Years)	8 years 9 months 18 days	8 years 10 months 24 days
Weighted-Average Remaining Contractual Life (Years), Options expected to vest - March 31, 2016	9 years 3 months 18 days
Weighted-Average Remaining Contractual Life (Years), Options exercisable - March 31, 2016	7 years 8 months 12 days
Aggregate Intrinsic Value
Aggregate Intrinsic Value, Outstanding	$ 19
Aggregate Intrinsic Value, Options expected to vest	$ 18

Stock-Based Compensation - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
2014 Stock Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average per share grant date fair value of options granted	$ 1.70	$ 5.07
2014 Stock Incentive Plan [Member] \| Employee Stock Options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	$ 691,000	$ 420,000
2014 Stock Incentive Plan [Member] \| Non Employee Awards [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	38,000	20,000
Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	$ 12,000	$ 0
Purchase price as percentage of stock price on offering period	85.00%
Offering period	6 months
Common stock purchased	17,185
Common stock purchase price per share	$ 2.38

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
	Mar. 31, 2016	Mar. 31, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected life		6 years
Risk-free interest rate, minimum	1.31%	1.45%
Risk-free interest rate, maximum	1.89%	1.69%
Expected volatility	61.00%
Expected volatility, minimum		61.00%
Expected volatility, maximum		63.00%
Non Employee Awards [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected life		8 years
Risk-free interest rate, minimum	1.70%
Risk-free interest rate, maximum	2.00%
Expected volatility		62.00%
Expected volatility, minimum	60.00%
Expected volatility, maximum	61.00%
Risk-free interest rate		1.86%
Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected life	5 years 10 months 24 days
Minimum [Member] \| Non Employee Awards [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected life	6 years 10 months 24 days
Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected life	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	9 years 8 months 12 days

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	Mar. 31, 2016	Dec. 31, 2015
Carrying Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	$ 59,341	$ 75,325
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	$ 59,341	$ 75,325