Document and Entity Information	3 Months Ended
Document and Entity Information	Mar. 31, 2015	May 01, 2015
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2015
Document Fiscal Year Focus	2015
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	Smaller Reporting Company
Entity Common Stock, Shares Outstanding		27,284,026

Condensed Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 56,316	$ 51,174
Accounts receivable, prepaid expenses, and other current assets	2,266	1,662
Total current assets	58,582	52,836
Property and equipment — Net	330	342
Other assets	469	215
Total	59,381	53,393
Current liabilities:
Current portion of loan payable	836	3,124
Accounts payable	1,682	1,255
Accrued expenses	2,736	3,648
Other liabilities	35	34
Total current liabilities	5,289	8,061
Long-term liabilities:
Loan payable — net of current portion	13,576
Non-current accrued interest	108
Other		7
Total long-term liabilities	13,684	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, 20,568,026 and 20,125,049 shares issued and outstanding at March 31, 2015 and December 31, 2014, respectively	2	2
Additional paid-in capital	170,615	167,104
Accumulated deficit	(130,209)	(121,781)
Total stockholders’ equity	40,408	45,325
Total	$ 59,381	$ 53,393

Condensed Consolidated Balance Sheets (Parenthetical) (USD $)	Mar. 31, 2015	Dec. 31, 2014
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	120,000,000	120,000,000
Common stock, shares issued	20,568,026	20,125,049
Common stock, shares outstanding	20,568,026	20,125,049

Condensed Consolidated Statements of Operations (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Income Statement [Abstract]
Revenue	$ 0	$ 47
Operating expenses:
Research and development	5,021	1,495
General and administrative	2,681	1,510
Total operating expenses	7,702	3,005
Other income (expense):
Interest income	3	1
Interest expense	(721)	(461)
Other expense	(8)
Decrease in value of preferred stock warrant liability		504
Total other (expense) income — net	(726)	44
Net loss attributable to common stockholders	$ (8,428)	$ (2,914)
Net loss per share attributable to common stockholders:
Basic and diluted	$ (0.41)	$ (3.70)
Weighted-average common shares outstanding:
Basic and diluted	20,350,557	786,986

Condensed Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Cash flows from operating activities:
Net loss	$ (8,428)	$ (2,914)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	440	148
Noncash rent expense	(6)	2
Change in carrying value of preferred stock warrant liability		(504)
Depreciation and amortization	41	36
Noncash interest expense	515	120
Changes in operating assets and liabilities:
Accounts receivable, prepaid expenses and other current assets	(120)	(1,019)
Accounts payable	378	1,246
Accrued expenses	(761)	(781)
Net cash used in operating activities	(7,941)	(3,666)
Cash flows from investing activities:
Purchases of property and equipment	(29)	(14)
Proceeds from sale of property and equipment		10
Net cash used in investing activities	(29)	(4)
Cash flows from financing activities:
Proceeds from sale of common stock	2,411	27
Proceeds from issuance of loans payable	15,000
Proceeds from issuance of convertible promissory notes		8,500
Payments on loans payable	(3,921)	(812)
Cash paid for debt issuance costs	(359)
Cash paid for deferred financing costs	(19)	(1,065)
Net cash provided by financing activities	13,112	6,650
Net increase in cash and cash equivalents	5,142	2,980
Cash and cash equivalents — Beginning of period	51,174	5,488
Cash and cash equivalents — End of period	56,316	8,468
Supplemental cash flow information — Interest paid	$ 163	$ 126

Nature of Business and Operations

3 Months Ended

Mar. 31, 2015

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.

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.

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 March 31, 2015 and the results of its operations and cash flows for the three months ended March 31, 2015 and 2014. Such adjustments are of a normal and recurring nature. The results for the three months ended March 31, 2015 are not indicative of the results for the year ending December 31, 2015, or for any future period.

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 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 increase in shares outstanding in 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.

Significant Accounting Policies

3 Months Ended

Mar. 31, 2015

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 Company’s Annual Report on Form 10-K.

Recent Accounting Pronouncements – In April 2015 Financial Accounting Standards Board (the “FASB”) issued Accounting Standards Update (“ASU”) 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.

- Definition

The entire disclosure for all significant accounting policies of the reporting entity.

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Net Loss Per Share Attributable to Common Stockholders

3 Months Ended

Mar. 31, 2015

Earnings Per Share [Abstract]

Net Loss Per Share Attributable to Common Stockholders

3.	NET LOSS PER SHARE ATTRIBUTABLE TO COMMON STOCKHOLDERS

Basic net loss per share attributable to common stockholders 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 in which the Company earns 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”). In 2014, the Company’s preferred stock participated in dividends declared by the Company and were therefore considered to be participating securities. Participating securities have the effect of diluting both basic and diluted earnings per share during periods in which the Company earns net income. During periods in which the Company incurs a net loss, the Company allocates no portion of the loss to participating securities because they had 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, warrants and shares of unvested restricted stock that are outstanding to the period, except where the inclusion of such nonparticipating 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 two-class 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,
	2015		2014
Options to purchase common stock		2,660,498		1,208,077
Warrants to purchase redeemable convertible preferred stock		—		128,663
Warrants to purchase common stock		300,564		—
Redeemable convertible preferred stock		—		6,826,004
Convertible notes payable		—		2,894,099

- Definition

The entire disclosure for earnings per share.

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Accrued Expenses

3 Months Ended

Mar. 31, 2015

Payables And Accruals [Abstract]

Accrued Expenses

4.	ACCRUED EXPENSES

Accrued expenses consist of the following:

	As of March 31, 2015		As of December 31, 2014
Accrued expenses	$	974	$	663
Accrued clinical trial costs		1,008		848
Accrued contract manufacturing expenses		158		580
Accrued compensation and benefits		502		983
Accrued interest		94		574
Total accrued expenses	$	2,736	$	3,648

Convertible Notes Payable to Shareholders

3 Months Ended

Mar. 31, 2015

Debt Disclosure [Abstract]

Convertible Notes Payable to Shareholders

5.	CONVERTIBLE NOTES PAYABLE TO SHAREHOLDERS

In August of 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 IPO in April 2014.

In February and March 2014, the Company issued convertible promissory notes in the original principal amount of $6,000,000 to existing investors and a convertible promissory note in the original principal amount of $2,500,000 to a new investor. All of 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 IPO 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 IPO.

- Definition

The entire disclosure for information about short-term and long-term debt arrangements, which includes amounts of borrowings under each line of credit, note payable, commercial paper issue, bonds indenture, debenture issue, own-share lending arrangements and any other contractual agreement to repay funds, and about the underlying arrangements, rationale for a classification as long-term, including repayment terms, interest rates, collateral provided, restrictions on use of assets and activities, whether or not in compliance with debt covenants, and other matters important to users of the financial statements, such as the effects of refinancing and noncompliance with debt covenants.

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Loan Agreements

3 Months Ended

Mar. 31, 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., or Hercules, the proceeds of which 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 make a final payment to the lender in the amount of 6.70% of the aggregate original principal amount advanced by the lender. The amount 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 in connection with the Hercules Loan Agreement:

	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 $10,000,000 in one or more advances by December 31, 2012. 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 was required to make an additional interest 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 was included in accrued expense in the accompanying 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. 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 March 31, 2015 and December 31, 2014, 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			March 2012			August 2012
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 Company determined the fair value of the warrant at the end of each subsequent reporting period using the Black-Scholes option pricing model until their conversion to warrants 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 warrants, or $0.2 million, was expensed as interest expense upon repayment of the loan in January 2015.

Stock Option Plan

3 Months Ended

Mar. 31, 2015

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock Option Plan

7.	STOCK OPTION PLAN

A summary of stock option activity for employee, director and nonemployee awards under all stock option plans during the three months ended March 31, 2015 is presented below:

	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		842,820			8.91
Exercised		(307,476	)		4.59
Forfeited		(1,022	)		5.73
Outstanding — March 31, 2015		2,660,498		$	6.33		7.3	$	7,716
Options expected to vest — March 31, 2015		1,561,898		$	7.14		9.5	$	3,368
Options exercisable — March 31, 2015		580,484		$	4.79		6.5	$	2,531

The weighted-average per share grant date fair value of options granted during the three months ended March 31, 2015 and 2014 was $5.07 and $5.95, 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, 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 $420,000 and $148,000 for the three months ended March 31, 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 months ended March 31, 2015 and 2014 are as follows:

	Three Months Ended March 31,
	2015	2014
Expected life	6 years	6 years
Risk-free interest rate	1.45%-1.69%	1.83%-2.00%
Expected volatility	61%-63%		60.00	%
Expected dividend rate	—%	—%

The Company recorded stock-based compensation expense related to nonemployee awards of $20,000 and $12,000 for the three months ended March 31, 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 months ended March 31, 2015 and 2014 were as follows:

	Three Months Ended March 31,
	2015			2014
Expected life	8 years			8 years
Risk-free interest rate		1.86	%	2.11%-2.63%
Expected volatility		62.00	%	56%-59%
Expected dividend rate	—%			—%

The Company did not grant any nonemployee stock option grants for the three months ended March 31, 2015 and 2014.

- Definition

The entire disclosure for compensation-related costs for equity-based compensation, which may include disclosure of policies, compensation plan details, allocation of equity compensation, incentive distributions, equity-based arrangements to obtain goods and services, deferred compensation arrangements, employee stock ownership plan details and employee stock purchase plan details.

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Fair Value Measurements

3 Months Ended

Mar. 31, 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, 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 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, 2015 and December 31, 2014, is as follows:

			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, 2015
Money market funds	$	55,844	$	—	$	55,844	$	—
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 have 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.

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Subsequent Events

3 Months Ended

Mar. 31, 2015

Subsequent Events [Abstract]

Subsequent Events

9.	SUBSEQUENT EVENT

On April 10, 2015, the Company closed an underwritten public offering (the “Secondary Offering”) of 6,716,000 shares of common stock, including 876,000 shares sold pursuant to the full exercise of the underwriters’ option to purchase additional shares, at a public offering price of $6.00 per share. The gross proceeds to the Company from the Secondary Offering were approximately $40.3 million, before deducting underwriting discounts and commissions and offering expenses payable by the Company.

Significant Accounting Policies (Policies)	3 Months Ended
Significant Accounting Policies (Policies)	Mar. 31, 2015
Accounting Policies [Abstract]
Recent Accounting Pronouncements	Recent Accounting Pronouncements – In April 2015 Financial Accounting Standards Board (the “FASB”) issued Accounting Standards Update (“ASU”) 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 (Tables)

3 Months Ended

Mar. 31, 2015

Earnings Per Share [Abstract]

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

	As of March 31,
	2015		2014
Options to purchase common stock		2,660,498		1,208,077
Warrants to purchase redeemable convertible preferred stock		—		128,663
Warrants to purchase common stock		300,564		—
Redeemable convertible preferred stock		—		6,826,004
Convertible notes payable		—		2,894,099

Accrued Expenses (Tables)

3 Months Ended

Mar. 31, 2015

Payables And Accruals [Abstract]

Schedule of Accrued Expenses

Accrued expenses consist of the following:

	As of March 31, 2015		As of December 31, 2014
Accrued expenses	$	974	$	663
Accrued clinical trial costs		1,008		848
Accrued contract manufacturing expenses		158		580
Accrued compensation and benefits		502		983
Accrued interest		94		574
Total accrued expenses	$	2,736	$	3,648

Loan Agreements (Tables)

3 Months Ended

Mar. 31, 2015

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 in connection with the Hercules Loan Agreement:

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

Loan and Security Agreement with Bank [Member] | Preferred 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 preferred stock warrants in connection with the loan and security agreement on the respective dates:

	Series D Preferred Stock Warrants
	December 2011			March 2012			August 2012
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	—			—			—

Stock Option Plan (Tables)

3 Months Ended

Mar. 31, 2015

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

A summary of stock option activity for employee, director and nonemployee awards under all stock option plans during the three months ended March 31, 2015 is presented below:

	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		842,820			8.91
Exercised		(307,476	)		4.59
Forfeited		(1,022	)		5.73
Outstanding — March 31, 2015		2,660,498		$	6.33		7.3	$	7,716
Options expected to vest — March 31, 2015		1,561,898		$	7.14		9.5	$	3,368
Options exercisable — March 31, 2015		580,484		$	4.79		6.5	$	2,531

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, 2015 and 2014 are as follows:

	Three Months Ended March 31,
	2015	2014
Expected life	6 years	6 years
Risk-free interest rate	1.45%-1.69%	1.83%-2.00%
Expected volatility	61%-63%		60.00	%
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, 2015 and 2014 were as follows:

	Three Months Ended March 31,
	2015			2014
Expected life	8 years			8 years
Risk-free interest rate		1.86	%	2.11%-2.63%
Expected volatility		62.00	%	56%-59%
Expected dividend rate	—%			—%

Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2015

Fair Value Disclosures [Abstract]

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

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

			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, 2015
Money market funds	$	55,844	$	—	$	55,844	$	—
December 31, 2014
Money market funds	$	50,541	$	—	$	50,541	$	—

Nature of Business and Operations - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	0 Months Ended		3 Months Ended
	May 07, 2014	Apr. 15, 2014	Mar. 31, 2015
Nature Of Business And Operations [Line Items]
Date of Company's incorporation			Nov. 28, 2005
IPO [Member]
Nature Of Business And Operations [Line Items]
Common stock issuance date			Apr. 15, 2014
Issuance of Common Stock from initial public offering, shares	1,069,715	8,500,000
Issuance/sale of stock, price per share	$ 7.00	$ 7.00
Proceeds from initial public offering, net	$ 59.9
Convertible preferred stock, shares issued upon conversion		9,728,237
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] \| Warrants To Purchase Preferred Stock Converted Into Warrants To Purchase Common Stock [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] \| Warrants To Purchase Preferred Stock Converted Into Warrants To Purchase Common Stock [Member] \| Common Stock Warrants [Member]
Nature Of Business And Operations [Line Items]
Warrant to purchase stock, number of securities called by warrants or rights		128,663

Net Loss Per Share Attributable to Common Stockholders - Potentially Dilutive Securities Excluded from Computation of Diluted Weighted-Average Shares Outstanding (Detail)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Redeemable Convertible Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted weighted-average shares outstanding		6,826,004
Options to Purchase Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted weighted-average shares outstanding	2,660,498	1,208,077
Warrants [Member] \| Redeemable Convertible Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted weighted-average shares outstanding		128,663
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
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		2,894,099

- Definition

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

+ References+ Details

Accrued Expenses - Schedule of Accrued Expenses (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Payables And Accruals [Abstract]
Accrued expenses	$ 974	$ 663
Accrued clinical trial costs	1,008	848
Accrued contract manufacturing expenses	158	580
Accrued compensation and benefits	502	983
Accrued interest	94	574
Total accrued expenses	$ 2,736	$ 3,648

- Definition

Carrying value as of the balance sheet date of obligations incurred through that date and payable arising from transactions not otherwise specified in the taxonomy. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

+ References+ Details

Convertible Notes Payable to Shareholders - Additional Information (Detail) (Convertible Notes Payable [Member], USD $)	1 Months Ended	3 Months Ended
	Apr. 30, 2014	Mar. 31, 2015	Dec. 31, 2014	Aug. 31, 2013
Debt Instrument [Line Items]
Debt instrument, Original principal amount				$ 8,824,000
Debt instrument stated interest rate			7.00%	7.00%
IPO closure date		2014-04-15
Debt instrument, Conversion Ratio	0.775
Loss on extinguishment of debt	(2,493,000)
Existing Investors [Member]
Debt Instrument [Line Items]
Debt instrument, Original principal amount			6,000,000
New Investor [Member]
Debt Instrument [Line Items]
Debt instrument, Original principal amount			$ 2,500,000

- Definition

Ratio applied to the conversion of debt instrument into equity with equity shares divided by debt principal amount.

+ References+ Details

Loan Agreements - Additional Information (Detail) (USD $)	3 Months Ended				1 Months Ended				3 Months Ended	6 Months Ended	1 Months Ended	3 Months Ended						0 Months Ended	3 Months Ended			0 Months Ended								0 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Jan. 31, 2015	Dec. 31, 2014	Jan. 31, 2015 Loan and Security Agreement with Lighthouse Capital Partners VI, L.P. [Member]	Aug. 31, 2012 Loan and Security Agreement with Lighthouse Capital Partners VI, L.P. [Member]	Mar. 31, 2012 Loan and Security Agreement with Lighthouse Capital Partners VI, L.P. [Member]	Dec. 31, 2011 Loan and Security Agreement with Lighthouse Capital Partners VI, L.P. [Member]	Mar. 31, 2015 Loan and Security Agreement with Lighthouse Capital Partners VI, L.P. [Member]	Aug. 31, 2012 Loan and Security Agreement with Lighthouse Capital Partners VI, L.P. [Member]	Dec. 31, 2011 Loan and Security Agreement with Lighthouse Capital Partners VI, L.P. [Member] Series D Convertible Preferred Stock [Member]	Mar. 31, 2015 Loan and Security Agreement with Lighthouse Capital Partners VI, L.P. [Member] Series D Convertible Preferred Stock [Member]	Dec. 31, 2014 Loan and Security Agreement with Lighthouse Capital Partners VI, L.P. [Member] Series D Convertible Preferred Stock [Member]	Aug. 31, 2012 Loan and Security Agreement with Lighthouse Capital Partners VI, L.P. [Member] Series D Convertible Preferred Stock [Member]	Mar. 31, 2012 Loan and Security Agreement with Lighthouse Capital Partners VI, L.P. [Member] Series D Convertible Preferred Stock [Member]	Apr. 30, 2014 Loan and Security Agreement with Lighthouse Capital Partners VI, L.P. [Member] Common Stock [Member]	Dec. 31, 2011 Maximum [Member] Loan and Security Agreement with Lighthouse Capital Partners VI, L.P. [Member] Series D Convertible Preferred Stock [Member]	Jan. 08, 2015 Loan and Security Agreement with Hercules Technology Growth Capital, Inc. [Member]	Mar. 31, 2015 Loan and Security Agreement with Hercules Technology Growth Capital, Inc. [Member]	Jan. 31, 2015 Loan and Security Agreement with Hercules Technology Growth Capital, Inc. [Member]	Jan. 08, 2015 Loan and Security Agreement with Hercules Technology Growth Capital, Inc. [Member] Common Stock [Member]	Jan. 08, 2015 Loan and Security Agreement with Hercules Technology Growth Capital, Inc. [Member] If Payment Occurs Within Twelve Months Of Closing Date [Member]	Jan. 08, 2015 Loan and Security Agreement with Hercules Technology Growth Capital, Inc. [Member] If Payment Occurs After Twelve Months But on or Prior to Twenty Four Months Following Closing Date [Member]	Jan. 08, 2015 Loan and Security Agreement with Hercules Technology Growth Capital, Inc. [Member] If Payment Occurs on or After Twenty Four Months Following Closing Date [Member[	Jan. 08, 2015 Loan and Security Agreement with Hercules Technology Growth Capital, Inc. [Member] Prime Rate [Member]	Jan. 08, 2015 Loan and Security Agreement with Hercules Technology Growth Capital, Inc. [Member] Borrowing One [Member]	Jan. 08, 2015 Loan and Security Agreement with Hercules Technology Growth Capital, Inc. [Member] Borrowing Two [Member]	Jan. 08, 2015 Loan and Security Agreement with Hercules Technology Growth Capital, Inc. [Member] Borrowing Three [Member]	Jan. 08, 2015 Loan and Security Agreement with Hercules Technology Growth Capital, Inc. [Member] Maximum [Member] Tranches	Jan. 08, 2015 Loan and Security Agreement with Hercules Technology Growth Capital, Inc. [Member] Minimum [Member]
Debt Instrument [Line Items]
Loan and security agreement, maximum borrowing capacity								$ 10,000,000										$ 26,000,000								$ 15,000,000	$ 5,000,000	$ 6,000,000
Amount of term loan facility required to be drawn																														3,000,000
Customary funding conditions minimum net cash proceeds required from issuance and sale of equity securities																		40,000,000
Number of tranches																													3
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%
Term loan facility, interest rate spread																									5.75%
Debt prepayment charge																						3.00%	2.00%	1.00%
Exercise price of warrant											$ 12.04										$ 6.05
Warrant to purchase stock, number of securities called by warrants or rights											29,067	66,436	66,436			66,436	66,436				137,521
Class of additional warrant or right number of securities called by warrants or rights																		34,380
Class of warrant or right, date until which warrants exercisable																		Jan. 08, 2020
Estimated fair value of warrant											284,000			178,000	182,000					659,000
Loan and security agreement, borrowings repayment period								36 months										30 months
Common stock, shares issued	20,568,026			20,125,049														135,501
Issuance/sale of stock, price per share																		$ 7.38
Proceeds from sale of common stock	2,411,000	27,000																1,000,000
Proceeds from loan payable	15,000,000					5,000,000	5,000,000			10,000,000
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
Accrued interest	94,000			574,000
Proceeds from repayments of notes payable					3,600,000
Warrant expiration date												2021-12
Warrant expiration period											10 years
Unamortized discount relating to warrants			$ 200,000

Loan Agreements - Fair Value of Preferred Stock Warrants Calculated using Black-Scholes Assumptions (Detail)	1 Months Ended			0 Months Ended
	Aug. 31, 2012 Loan and Security Agreement with Lighthouse Capital Partners VI, L.P. [Member] Series D Convertible Preferred Stock [Member]	Mar. 31, 2012 Loan and Security Agreement with Lighthouse Capital Partners VI, L.P. [Member] Series D Convertible Preferred Stock [Member]	Dec. 31, 2011 Loan and Security Agreement with Lighthouse Capital Partners VI, L.P. [Member] Series D Convertible Preferred Stock [Member]	Jan. 08, 2015 Loan and Security Agreement with Hercules Technology Growth Capital, Inc. [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	5 years
Volatility rate	80.00%	80.00%	80.00%	61.00%
Risk-free interest rate	1.68%	2.17%	1.98%	1.50%

Stock Option Plan -Summary of Stock Option Activity for Employee, Director and Nonemployee Awards (Detail) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2013	Dec. 31, 2014
Number of shares
Number of Shares, Outstanding	2,126,176
Number of Shares, Granted	842,820
Number of Shares, Exercised	(307,476)
Number of Shares, Forfeited	(1,022)
Number of Shares, Outstanding	2,660,498
Number of Shares, Options expected to vest	1,561,898
Number of Shares, Options exercisable	580,484
Weighted-Average Exercise Price
Weighted-Average Exercise Price, Outstanding	$ 4.97
Weighted-Average Exercise Price, Granted	$ 8.91
Weighted-Average Exercise Price, Exercised	$ 4.59
Weighted-Average Exercise Price, Forfeited	$ 5.73
Weighted-Average Exercise Price, Outstanding	$ 6.33
Weighted-Average Exercise Price, Options expected to vest	$ 7.14
Weighted-Average Exercise Price, Options exercisable	$ 4.79
Weighted-Average Remaining Contractual Life (Years)
Weighted-Average Remaining Contractual Life (Years)	7 years 3 months 18 days	6 years 8 months 12 days
Weighted-Average Remaining Contractual Life (Years), Options expected to vest - December 31, 2014	9 years 6 months
Weighted-Average Remaining Contractual Life (Years), Options exercisable - December 31, 2014	6 years 6 months
Aggregate Intrinsic Value
Aggregate Intrinsic Value, Outstanding	$ 7,716		$ 2,701
Aggregate Intrinsic Value, Options expected to vest	3,368
Aggregate Intrinsic Value, Options exercisable	$ 2,531

Stock Option Plan - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average per share grant date fair value of options granted	$ 5.07	$ 5.95
Number of Shares, Granted	842,820
Employee Awards [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	$ 420,000	$ 148,000
Non Employee Awards [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	$ 20,000	$ 12,000
Number of Shares, Granted	0	0

Stock Option Plan - 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, 2015	Mar. 31, 2014
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected life	6 years	6 years
Risk-free interest rate, minimum	1.45%	1.83%
Risk-free interest rate, maximum	1.69%	2.00%
Expected volatility		60.00%
Expected volatility, minimum	61.00%
Expected volatility, maximum	63.00%
Expected dividend rate	0.00%	0.00%
Non Employee Awards [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected life	8 years	8 years
Risk-free interest rate, minimum		2.11%
Risk-free interest rate, maximum		2.63%
Expected volatility	62.00%
Expected volatility, minimum		56.00%
Expected volatility, maximum		59.00%
Expected dividend rate	0.00%	0.00%
Risk-free interest rate	1.86%

Fair Value Measurements - Summary of Financial Assets and Liabilities Measured on Recurring Basis at Fair Value (Detail) (USD $)	Mar. 31, 2015	Mar. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	$ 55,844	$ 50,541
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	$ 55,844	$ 50,541

Subsequent Event - Additional Information (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		0 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Apr. 10, 2015 Subsequent Event [Member] Secondary Offering [Member]	Apr. 10, 2015 Subsequent Event [Member] Secondary Offering [Member] Option Exercised by Underwriter [Member]
Subsequent Event [Line Items]
Issuance of common stock, shares			6,716,000	876,000
Common share offering price, per share			$ 6.00
Proceeds from sale of common stock	$ 2,411	$ 27	$ 40,300