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Document and Entity Information - shares	9 Months Ended
Document and Entity Information - shares	Sep. 30, 2016	Oct. 31, 2016
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2016
Document Fiscal Year Focus	2016
Document Fiscal Period Focus	Q3
Trading Symbol	CERU
Entity Registrant Name	CERULEAN PHARMA INC.
Entity Central Index Key	0001401914
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		27,435,680

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 38,058	$ 75,908
Accounts receivable, prepaid expenses, and other current assets	1,146	1,394
Total current assets	39,204	77,302
Property and equipment, net	699	576
Other assets	230	347
Total	40,133	78,225
Current liabilities:
Current portion of loan payable	8,192	7,652
Accounts payable	1,778	2,226
Accrued expenses	5,919	6,459
Total current liabilities	15,889	16,337
Long-term liabilities:
Loan payable, net of current portion	6,550	12,672
Other long-term liabilities	1,075	473
Total long-term liabilities	7,625	13,145
Commitments and contingencies
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, 27,384,492 and 27,346,780 shares issued and outstanding at September 30, 2016 and December 31, 2015, respectively	3	3
Additional paid-in capital	212,351	210,115
Accumulated deficit	(195,735)	(161,375)
Total stockholders’ equity	16,619	48,743
Total	$ 40,133	$ 78,225

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 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	27,384,492	27,346,780
Common stock, shares outstanding	27,384,492	27,346,780

Condensed Consolidated Statements of Operations (unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Operating expenses:
Research and development	$ 7,089	$ 7,092	$ 24,381	$ 18,791
General and administrative	2,374	2,954	8,265	8,352
Total operating expenses	9,463	10,046	32,646	27,143
Other income (expense):
Interest income	25	4	66	8
Interest expense	(521)	(509)	(1,781)	(1,743)
Other income (expense)			1	(8)
Total other expense, net	(496)	(505)	(1,714)	(1,743)
Net loss attributable to common stockholders	$ (9,959)	$ (10,551)	$ (34,360)	$ (28,886)
Net loss per share attributable to common stockholders:
Basic and diluted	$ (0.36)	$ (0.39)	$ (1.26)	$ (1.17)
Weighted-average common shares outstanding:
Basic and diluted	27,383,376	27,307,103	27,370,044	24,785,833

Condensed Consolidated Statements of Cash Flows (unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Cash flows from operating activities:
Net loss	$ (34,360)	$ (28,886)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	2,158	1,731
Noncash rent expense	143	(24)
Depreciation and amortization	195	129
Amortization of debt discount and deferred financing costs	335	1,020
Loss on disposal of property and equipment	4
Changes in operating assets and liabilities:
Accounts receivable, prepaid expenses and other current assets	248	185
Accounts payable	(271)	904
Accrued expenses	(113)	1,236
Net cash used in operating activities	(31,661)	(23,705)
Cash flows from investing activities:
Purchases of property and equipment	(499)	(141)
Decrease (increase) in restricted cash	117	(230)
Net cash used in investing activities	(382)	(371)
Cash flows from financing activities:
Proceeds from sale of common stock	78	2,628
Proceeds from public stock offering, net of issuance costs		37,185
Proceeds from issuance of loans payable		15,000
Payments on loans payable	(5,885)	(3,921)
Cash paid for debt issuance costs		(359)
Net cash (used in) provided by financing activities	(5,807)	50,533
Net (decrease) increase in cash and cash equivalents	(37,850)	26,457
Cash and cash equivalents — Beginning of period	75,908	51,174
Cash and cash equivalents — End of period	38,058	77,631
Supplemental cash flow information — Interest paid	$ 1,026	$ 723

Nature of Business and Operations

9 Months Ended

Sep. 30, 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 September 30, 2016 and the results of its operations for the three and nine months ended September 30, 2016 and 2015 and cash flows for the nine months ended September 30, 2016 and 2015. Such adjustments are of a normal and recurring nature. The results for the three and nine months ended September 30, 2016, are not indicative of the results for the year ending December 31, 2016, or for any future period.

As a clinical stage entity, the Company has incurred historical operating losses resulting in an accumulated deficit of $195.7 million at September 30, 2016. The Company expects to continue to incur significant expenses and increasing operating losses for at least several years. To date, 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. Following a reduction in force initiated in August 2016, the Company believes its cash and cash equivalents of approximately $38.1 million at September 30, 2016, together with $1.0 million in proceeds from an initial sale of common stock to Aspire Capital Fund LLC in October 2016, and a $5.0 million upfront payment under the Company’s collaboration agreement with Novartis Institutes for BioMedical Research, Inc. received in October 2016 (see Note 8, “Subsequent Events”), are sufficient to fund its planned operations for at least twelve months following the date of this report. The Company will need to raise additional capital to continue to fund its long-term operations. Should its operating plan change further, or prove to be inaccurate, then the Company will be required to reassess its operating capital needs. However, there can be no assurance that the Company will have the cash resources to fund its operating plan or that additional funding will be available on terms acceptable to it, or at all.

Significant Accounting Policies

9 Months Ended

Sep. 30, 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 August 2016, the Financial Accounting Standards Board (the “FASB”) issued Accounting Standards Update 2016-15, “Statement of Cash Flows (Topic 230)” (“ASU 2016-15”). ASU 2016-15 makes cash payments for debt prepayment or debt extinguishment costs to be classified as cash outflows for financing activities. The standard is effective for financial statements issued for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years. The Company is evaluating the impact of the new guidance.

In March 2016, the FASB issued Accounting Standards Update 2016-09, “Compensation – Stock Compensation (Topic 718)” (“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, 2016, 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 (Topic 842)” (“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, “Presentation of Financial Statements – Going Concern (Subtopic 205-40): 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

9 Months Ended

Sep. 30, 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 September 30,
	2016		2015
Options to purchase common stock		4,554,153		2,521,772
Warrants to purchase common stock		300,564		300,564

Accrued Expenses

9 Months Ended

Sep. 30, 2016

Payables And Accruals [Abstract]

Accrued Expenses

4.	ACCRUED EXPENSES

Accrued expenses consist of the following (in thousands):

	As of September 30, 2016		As of December 31, 2015
Accrued clinical trial costs	$	2,834	$	2,631
Accrued contract manufacturing expenses		801		945
Accrued compensation and benefits		1,319		1,864
Accrued interest		92		136
Accrued legal fees		301		130
Other accrued expenses		572		753
Total accrued expenses	$	5,919	$	6,459

Loan Agreements

9 Months Ended

Sep. 30, 2016

Debt Disclosure [Abstract]

Loan Agreements

5.	LOAN AGREEMENTS

On January 8, 2015, the Company entered into a loan and security agreement with Hercules Technology Growth Capital, Inc. (“Hercules”) to borrow up to $26.0 million (the “Hercules Loan Agreement”). The proceeds were used to repay the Company’s then-existing term loan facility with Lighthouse Capital Partners VI, L.P. (“Lighthouse Capital”) and for general corporate and working capital purposes. At September 30, 2016 and December 31, 2015, the Company had $15.1 million and $21.0 million, respectively, outstanding under the Hercules Loan Agreement.

The Hercules Loan Agreement will mature on July 1, 2018. Each advance under the Hercules Loan Agreement 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 Hercules Loan Agreement 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. Failure to make payments or comply with other covenants as stated in the Hercules Loan Agreement could result in an event of default and acceleration of amounts due. In such case, the Company may not be able to make accelerated payments, and Hercules could seek to enforce security interests in the collateral securing such indebtedness, which includes substantially all of the Company’s assets other than its intellectual property. 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.

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

9 Months Ended

Sep. 30, 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.

Stock Options

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. A summary of stock option activity for employee, director and nonemployee awards under all stock option plans during the nine months ended September 30, 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 at January 1, 2016		3,454,926		$	5.39		8.9	$	—
Granted		1,570,070		$	1.88
Exercised		—			—
Forfeited		(470,843	)	$	4.27
Outstanding at September 30, 2016		4,554,153		$	4.29		8.4	$	1,620
Options exercisable at September 30, 2016		1,453,813		$	5.66		6.8	$	135
Options vested and expected to vest at September 30, 2016		4,407,931		$	4.31		8.4	$	1,578

The weighted-average per share grant date fair value of options granted during the nine months ended September 30, 2016 and 2015 was $1.09 and $4.22, 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 $685,000 and $773,000 for the three months ended September 30, 2016 and 2015, respectively, and $2.1 million and $1.6 million for the nine months ended September 30, 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 and nine months ended September 30, 2016 and 2015 are as follows:

	Three Months Ended September 30,		Nine Months Ended September 30,
	2016	2015	2016	2015
Expected life	5.4-6.0 years	6.0-6.1 years	5.4-6.1 years	5.4-6.1 years
Risk-free interest rate	1.2%-1.3%	1.7%	1.2%-1.9%	1.5%-2.0%
Expected volatility	68%	61%	61%-68%	61%-63%
Expected dividend rate	—%	—%	—%	—%

The Company recorded stock-based compensation expense related to nonemployee awards of $11,000 and $63,000 for the three months ended September 30, 2016 and 2015, respectively and $63,000 and $135,000 for the nine months ended September 30, 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 fair value of the grants is being expensed over the vesting period of the options on a straight-line basis as the services are being provided. The Black-Scholes assumptions used to estimate fair value for the three and nine months ended September 30, 2016 and 2015 were as follows:

	Three Months Ended September 30,		Nine Months Ended September 30,
	2016	2015	2016	2015
Expected life	5.0-6.0 years	10 years	5.0-6.0 years	10 years
Risk-free interest rate	1.1%-1.3%	2.1%	1.1%-1.3%	2.0%-2.1%
Expected volatility	68%	59%	68%	60%
Expected dividend rate	—%	—%	—%	—%

During the nine months ended September 30, 2016 and 2015, the Company granted nonemployee stock options to purchase 135,000 and 192,000 shares, respectively, of the Company’s common stock. The weighted-average exercise price and the weighted-average grant date fair value of nonemployee stock options granted for the nine months ended September 30, 2016 was $1.09 per share and $0.61 per share, respectively, and for the nine months ended September 30, 2015 was $5.28 per share and $2.33 per share, respectively. On September 4, 2015, nonemployee stock options to purchase 90,000 shares of the Company’s common stock were converted to employee stock options upon the appointment of the Company’s Chief Medical Officer who had been serving as a consultant to the Company until his appointment. The exercise price and the fair value of these stock options is $4.71 per share and $2.71 per share, respectively.

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 nine months ended September 30, 2016, 37,712 shares of common stock were purchased under the ESPP at a weighted average price of $2.07 per share. The stock-based compensation expense related to the ESPP for the three and nine months ended September 30, 2016 was $5,000 and $29,000, respectively, and was $13,000 for each of the three and nine months ended September 30, 2015.

- 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.

+ References + Details

Fair Value Measurements

9 Months Ended

Sep. 30, 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 (unadjusted) in active markets that are accessible at the market date for identical unrestricted assets or liabilities.

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

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

A summary of the financial assets and liabilities that are measured on a recurring basis at fair value as of September 30, 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)
September 30, 2016
Money market funds	$	37,139	$	—	$	37,139	$	—
December 31, 2015
Money market funds	$	75,325	$	—	$	75,325	$	—

The Company believes that its debt obligations bear interest at rates which approximate prevailing market rates for instruments with similar characteristics and, accordingly, the carrying values for these instruments approximate fair value. 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

Restructuring

9 Months Ended

Sep. 30, 2016

Restructuring And Related Activities [Abstract]

Restructuring

8.	RESTRUCTURING

In August 2016, the Company announced its plan to reduce its workforce by approximately 48%. This workforce reduction is designed to reduce operating expenses while the company refocuses its clinical strategy for CRLX101.

The Company recorded approximately $300,000 of total pre-tax charges recorded to research and development expense in the quarter ended September 30, 2016 in connection with the restructuring. Of this total, $274,000 was attributed to contractual termination benefits which were provided for once it was determined that such costs were both probable and estimable in accordance with the provisions of FASB Accounting Standard Codification 712, “Compensation—Nonretirement Postemployment Benefits”, and $26,000 was charged for discretionary termination benefits upon notification of the affected employees in accordance with ASC 420, “Exit or Disposal Cost Obligations”. Substantially all of the restructuring costs associated with the workforce reduction are expected to be paid by March 31, 2017.

Subsequent Events

9 Months Ended

Sep. 30, 2016

Subsequent Events [Abstract]

Subsequent Events

9.	SUBSEQUENT EVENTS

On October 14, 2016, the Company entered into a common stock purchase agreement (the “Purchase Agreement”) with Aspire Capital Fund, LLC, (“Aspire Capital”), which provides that, upon the terms and subject to the conditions and limitations set forth therein, Aspire Capital is committed to purchase up to an aggregate of $20.0 million of shares of the Company’s common stock over a term of 24 months from the execution of the Purchase Agreement. In consideration for entering into the Purchase Agreement, the Company issued to Aspire Capital 700,000 shares of the Company’s common stock. Immediately following the execution of the Purchase Agreement, the Company made an initial sale to Aspire Capital under the Purchase Agreement of 800,000 shares of common stock at a price of $1.25 per share, for proceeds of $1.0 million.

On October 18, 2016, the Company entered into a research collaboration agreement (the “Collaboration Agreement”) with Novartis Institutes for BioMedical Research, Inc. (“Novartis”). Under the Collaboration Agreement, the Company will create NDC candidates using its Dynamic Tumor Targeting Platform and Novartis-selected active pharmaceutical ingredients, and Novartis will be responsible for the development and commercialization of NDC products resulting from the collaborative research efforts. The initial research term of the Collaboration Agreement is two years which may be extended for up to two additional one-year terms. The Company received a $5.0 million upfront payment under the Collaboration Agreement, and is entitled to receive funding from Novartis for up to five full-time employees of the Company to be engaged in activities under the collaboration during the research term. The Company may also receive additional research, development, regulatory and sales milestone payments, as well as royalties on net sales of any NDC product commercialized by Novartis.

Significant Accounting Policies (Policies)	9 Months Ended
Significant Accounting Policies (Policies)	Sep. 30, 2016
Accounting Policies [Abstract]
Recent Accounting Pronouncements	Recent Accounting Pronouncements – In August 2016, the Financial Accounting Standards Board (the “FASB”) issued Accounting Standards Update 2016-15, “Statement of Cash Flows (Topic 230)” (“ASU 2016-15”). ASU 2016-15 makes cash payments for debt prepayment or debt extinguishment costs to be classified as cash outflows for financing activities. The standard is effective for financial statements issued for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years. The Company is evaluating the impact of the new guidance. In March 2016, the FASB issued Accounting Standards Update 2016-09, “Compensation – Stock Compensation (Topic 718)” (“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, 2016, 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 (Topic 842)” (“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, “Presentation of Financial Statements – Going Concern (Subtopic 205-40): 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)

9 Months Ended

Sep. 30, 2016

Earnings Per Share [Abstract]

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

	As of September 30,
	2016		2015
Options to purchase common stock		4,554,153		2,521,772
Warrants to purchase common stock		300,564		300,564

Accrued Expenses (Tables)

9 Months Ended

Sep. 30, 2016

Payables And Accruals [Abstract]

Schedule of Accrued Expenses

Accrued expenses consist of the following (in thousands):

	As of September 30, 2016		As of December 31, 2015
Accrued clinical trial costs	$	2,834	$	2,631
Accrued contract manufacturing expenses		801		945
Accrued compensation and benefits		1,319		1,864
Accrued interest		92		136
Accrued legal fees		301		130
Other accrued expenses		572		753
Total accrued expenses	$	5,919	$	6,459

Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2016

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 nine months ended September 30, 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 at January 1, 2016		3,454,926		$	5.39		8.9	$	—
Granted		1,570,070		$	1.88
Exercised		—			—
Forfeited		(470,843	)	$	4.27
Outstanding at September 30, 2016		4,554,153		$	4.29		8.4	$	1,620
Options exercisable at September 30, 2016		1,453,813		$	5.66		6.8	$	135
Options vested and expected to vest at September 30, 2016		4,407,931		$	4.31		8.4	$	1,578

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

The assumptions used in the Black-Scholes option-pricing model for stock options granted to employees and to directors in respect of board services during the three and nine months ended September 30, 2016 and 2015 are as follows:

	Three Months Ended September 30,		Nine Months Ended September 30,
	2016	2015	2016	2015
Expected life	5.4-6.0 years	6.0-6.1 years	5.4-6.1 years	5.4-6.1 years
Risk-free interest rate	1.2%-1.3%	1.7%	1.2%-1.9%	1.5%-2.0%
Expected volatility	68%	61%	61%-68%	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 and nine months ended September 30, 2016 and 2015 were as follows:

	Three Months Ended September 30,		Nine Months Ended September 30,
	2016	2015	2016	2015
Expected life	5.0-6.0 years	10 years	5.0-6.0 years	10 years
Risk-free interest rate	1.1%-1.3%	2.1%	1.1%-1.3%	2.0%-2.1%
Expected volatility	68%	59%	68%	60%
Expected dividend rate	—%	—%	—%	—%

Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 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 September 30, 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)
September 30, 2016
Money market funds	$	37,139	$	—	$	37,139	$	—
December 31, 2015
Money market funds	$	75,325	$	—	$	75,325	$	—

Nature of Business and Operations - Additional Information (Detail) - USD ($) $ in Thousands		1 Months Ended	9 Months Ended
	Oct. 14, 2016	Oct. 31, 2016	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015	Dec. 31, 2014
Nature Of Business And Operations [Line Items]
Date of Company's incorporation			Nov. 28, 2005
Accumulated deficit			$ 195,735		$ 161,375
Cash and cash equivalents			38,058	$ 77,631	$ 75,908	$ 51,174
Proceeds from sale of common stock			$ 78	$ 2,628
Subsequent Events [Member] \| Aspire Capital Fund, LLC [Member] \| Initial Sale Under Stock Purchase Agreement [Member]
Nature Of Business And Operations [Line Items]
Proceeds from sale of common stock	$ 1,000	$ 1,000
Subsequent Events [Member] \| Novartis Institutes for BioMedical Research, Inc [Member] \| Collaboration Agreement [Member]
Nature Of Business And Operations [Line Items]
Upfront payment received		$ 5,000

Net Loss Per Share Attributable to Common Stockholders - Potentially Dilutive Securities Excluded from Computation of Diluted Weighted-Average Shares Outstanding (Detail) - shares	9 Months Ended
	Sep. 30, 2016	Sep. 30, 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	4,554,153	2,521,772
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	Sep. 30, 2016	Dec. 31, 2015
Payables And Accruals [Abstract]
Accrued clinical trial costs	$ 2,834	$ 2,631
Accrued contract manufacturing expenses	801	945
Accrued compensation and benefits	1,319	1,864
Accrued interest	92	136
Accrued legal fees	301	130
Other accrued expenses	572	753
Total accrued expenses	$ 5,919	$ 6,459

Loan Agreements - Additional Information (Detail) - USD ($)		1 Months Ended				6 Months Ended	9 Months Ended
	Jan. 08, 2015	Jan. 31, 2015	Aug. 31, 2012	Mar. 31, 2012	Dec. 31, 2011	Aug. 31, 2012	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015	Apr. 30, 2014
Debt Instrument [Line Items]
Proceeds from loan payable								$ 15,000,000
Loan and Security Agreement with Lighthouse Capital [Member] \| Loans payable [Member]
Debt Instrument [Line Items]
Loan and security agreement, maximum borrowing capacity					$ 10,000,000
Proceeds from loan payable			$ 5,000,000	$ 5,000,000		$ 10,000,000
Loan and security agreement, borrowings repayment period					36 months
Debt instrument stated interest rate					8.25%
Loan and security agreement, borrowings repayment start date					Dec. 01, 2012
Line of credit facility, additional interest payment							$ 600,000
Repayments of notes payable		$ 3,600,000
Unamortized discount 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					$ 12.04
Warrant expiration date					2021-12
Warrant expiration period					10 years
Loan and Security Agreement with Lighthouse Capital [Member] \| Loans payable [Member] \| Series D Convertible Preferred Stock [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Warrant to purchase stock, number of securities called by warrants or rights					66,436
Loan and Security Agreement with Lighthouse Capital [Member] \| Common Stock [Member] \| Loans payable [Member]
Debt Instrument [Line Items]
Warrant to purchase stock, number of securities called by warrants or rights										66,436
Hercules Technology Growth Capital, Inc. [Member] \| Hercules Loan Agreement [Member]
Debt Instrument [Line Items]
Loan and security agreement, maximum borrowing capacity	$ 26,000,000
Amount outstanding under the loan and security agreement							$ 15,100,000		$ 21,000,000
Loan and security agreement, maturity date	Jul. 01, 2018
Loan and security agreement, interest rate terms							The Hercules Loan Agreement will mature on July 1, 2018. Each advance under the Hercules Loan Agreement 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 Hercules Loan Agreement provided for interest-only payments on a monthly basis until December 31, 2015.
Loan and security agreement, covenants description							Failure to make payments or comply with other covenants as stated in the Hercules Loan Agreement could result in an event of default and acceleration of amounts due. In such case, the Company may not be able to make accelerated payments, and Hercules could seek to enforce security interests in the collateral securing such indebtedness, which includes substantially all of the Company’s assets other than its intellectual property.
Final payment as percentage of aggregate original principal amount	6.70%
Loan and security agreement, interest rate	7.30%
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] \| Common Stock [Member]
Debt Instrument [Line Items]
Exercise price of warrant	$ 6.05
Warrant to purchase stock, number of securities called by warrants or rights	171,901
Hercules Technology Growth Capital, Inc. [Member] \| Hercules Loan Agreement [Member] \| Prime Rate [Member]
Debt Instrument [Line Items]
Loan and security agreement, interest rate spread	5.75%

Stock-Based Compensation - Summary of Stock Option Activity for Employee, Director and Nonemployee Awards (Detail) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2015
Number of shares
Number of Shares, Outstanding	3,454,926
Number of Shares, Granted	1,570,070
Number of Shares, Forfeited	(470,843)
Number of Shares, Outstanding	4,554,153	3,454,926
Number of Shares, Options exercisable	1,453,813
Number of Shares, Options vested and expected to vest	4,407,931
Weighted-Average Exercise Price
Weighted-Average Exercise Price, Outstanding	$ 5.39
Weighted-Average Exercise Price, Granted	1.88
Weighted-Average Exercise Price, Forfeited	4.27
Weighted-Average Exercise Price, Outstanding	4.29	$ 5.39
Weighted-Average Exercise Price, Options exercisable	5.66
Weighted-Average Exercise Price, Options vested and expected to vest	$ 4.31
Weighted-Average Remaining Contractual Life (Years)
Weighted-Average Remaining Contractual Life (Years)	8 years 4 months 24 days	8 years 10 months 24 days
Weighted-Average Remaining Contractual Life (Years), Options exercisable at September 30, 2016	6 years 9 months 18 days
Weighted-Average Remaining Contractual Life (Years), Options vested and expected to vest at September 30, 2016	8 years 4 months 24 days
Aggregate Intrinsic Value
Aggregate Intrinsic Value, Outstanding	$ 1,620
Aggregate Intrinsic Value, Options exercisable	135
Aggregate Intrinsic Value, Options vested and expected to vest	$ 1,578

Stock-Based Compensation - Additional Information (Detail) - USD ($)		3 Months Ended		9 Months Ended
	Sep. 04, 2015	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Shares, Granted				1,570,070
Weighted-Average Exercise Price, Options exercisable		$ 5.66		$ 5.66
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				1.09	$ 4.22
2014 Stock Incentive Plan [Member] \| Non Employee Awards [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average per share grant date fair value of options granted	$ 2.71			$ 0.61	$ 2.33
Number of Shares, Granted	90,000			135,000	192,000
Weighted-Average Exercise Price, Options exercisable	$ 4.71	$ 1.09	$ 5.28	$ 1.09	$ 5.28
2014 Stock Incentive Plan [Member] \| Employee Stock Options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense		$ 685,000	$ 773,000	$ 2,100,000	$ 1,600,000
2014 Stock Incentive Plan [Member] \| Non Employee Awards [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense		11,000	63,000	63,000	135,000
Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense		$ 5,000	$ 13,000	$ 29,000	$ 13,000
Purchase price as percentage of stock price on offering period				85.00%
Offering period				6 months
Common stock purchased				37,712
Common stock purchase price per share		$ 2.07		$ 2.07

Stock-Based Compensation - Summary of Assumptions Used in Black-Scholes Option-Pricing Model for Stock Options Granted to Employees, Directors and Non Employees (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate		1.70%
Risk-free interest rate, minimum	1.20%		1.20%	1.50%
Risk-free interest rate, maximum	1.30%		1.90%	2.00%
Expected volatility	68.00%	61.00%
Expected volatility, minimum			61.00%	61.00%
Expected volatility, maximum			68.00%	63.00%
Non Employee Awards [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected life		10 years		10 years
Risk-free interest rate		2.10%
Risk-free interest rate, minimum	1.10%		1.10%	2.00%
Risk-free interest rate, maximum	1.30%		1.30%	2.10%
Expected volatility	68.00%	59.00%	68.00%	60.00%
Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected life	5 years 4 months 24 days	6 years	5 years 4 months 24 days	5 years 4 months 24 days
Minimum [Member] \| Non Employee Awards [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected life	5 years		5 years
Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected life	6 years	6 years 1 month 6 days	6 years 1 month 6 days	6 years 1 month 6 days
Maximum [Member] \| Non Employee Awards [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected life	6 years		6 years

Fair Value Measurements - Summary of Financial Assets and Liabilities Measured on Recurring Basis at Fair Value (Detail) - Fair Value, Measurements, Recurring [Member] - Money Market Funds [Member] - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Carrying Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	$ 37,139	$ 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	$ 37,139	$ 75,325

Restructuring - Additional Information (Detail) - USD ($)		3 Months Ended	9 Months Ended
	Aug. 31, 2016	Sep. 30, 2016	Sep. 30, 2016
Restructuring Cost And Reserve [Line Items]
Percentage of workforce reduced	48.00%
Restructuring costs expected payment date			Mar. 31, 2017
Research and Development Expense [Member]
Restructuring Cost And Reserve [Line Items]
Pre-tax restructuring charges		$ 300,000
Contractual termination benefits cost		274,000
Discretionary termination benefits cost		$ 26,000

Subsequent Events - Additional Information (Detail)			1 Months Ended	9 Months Ended
Subsequent Events - Additional Information (Detail)	Oct. 18, 2016 Employee	Oct. 14, 2016 USD ($) $ / shares shares	Oct. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)
Subsequent Event [Line Items]
Proceeds from common stock issued				$ 78,000	$ 2,628,000
Aspire Capital Fund, LLC [Member] \| Stock Purchase Agreement [Member] \| Subsequent Events [Member]
Subsequent Event [Line Items]
Stock purchase term		24 months
Number of shares issued \| shares		700,000
Aspire Capital Fund, LLC [Member] \| Stock Purchase Agreement [Member] \| Subsequent Events [Member] \| Maximum [Member]
Subsequent Event [Line Items]
Purchase of common stock aggregate commitment amount		$ 20,000,000
Aspire Capital Fund, LLC [Member] \| Initial Sale Under Stock Purchase Agreement [Member] \| Subsequent Events [Member]
Subsequent Event [Line Items]
Number of shares issued \| shares		800,000
Common stock price per share \| $ / shares		$ 1.25
Proceeds from common stock issued		$ 1,000,000	$ 1,000,000
Novartis Institutes for BioMedical Research, Inc [Member] \| Subsequent Events [Member] \| Collaboration Agreement [Member]
Subsequent Event [Line Items]
Upfront payment received			$ 5,000,000
Initial research term of agreement	2 years
Number of full-time employees engaged in research activities under the collaboration \| Employee	5
Research term of the agreement, description	The initial research term of the agreement is two years which may be extended for up to two additional one-year terms.