Collaboration Agreement - Additional Information (Detail) (USD $)	1 Months Ended				3 Months Ended								12 Months Ended			1 Months Ended	0 Months Ended	7 Months Ended	1 Months Ended
	May 31, 2014	Dec. 31, 2013	Oct. 31, 2011	Apr. 30, 2010	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014 Candidate Licensed_Program	Dec. 31, 2013	Dec. 31, 2012	Jul. 31, 2014	Jul. 31, 2014	Jul. 31, 2014	Jul. 31, 2013
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Agreement amended date				2011-10
Amended collaboration expiration date		2015-04		2014-04									2016-04	2015-04
Discovery phase years				2 years
Term of the initial discovery period before amendment to extend		4 years	3 years										5 years	4 years
Term of extended period after amendment of the initial discovery period		5 years	4 years										6 years	5 years
Eligible payment to be received from extension of the discovery phase		$ 20,000,000			$ 20,000,000				$ 20,000,000				$ 20,000,000	$ 20,000,000
Date of extension of discovery phase													2015-06	2014-05
Number of candidates confirmed by the Joint Research Committee													2
Number of licensed programs type under collaboration agreements													3
Period considered for agreement termination notice													90 days
Upfront payment received													121,200,000
Series B convertible preferred stock, purchased		0			0				0				0	0
Reverse stock split													1-for-2.75
Reverse stock split ratio													2.75
Payment made in pursuant to the amendment	20,000,000		20,000,000										20,000,000
Collaboration revenue					14,636,000	33,900,000	8,411,000	8,411,000	6,744,000	6,268,000	6,268,000	6,268,000	65,358,000	25,548,000	25,106,000
Recognized revenue to extension													0
Achievement of an early clinical development milestone event					22,500,000								22,500,000
Dosing of the last patient in a Company-sponsored					25,000,000								25,000,000
Development cost reimbursed													26,600,000
Collaboration receivable					6,500,000								6,500,000
Celgene [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payment upon achievement of a specified clinical development milestone event					10,000,000								10,000,000			10,000,000	10,000,000	10,000,000
Milestone payment reimbursement, percentage													50.00%			50.00%
Milestone or royalty payments received													0
Celgene [Member] | Split License [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recognition, selling price																	21,200,000
Celgene [Member] | In Process Research and Development [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recognition, selling price													50,800,000			13,600,000		42,700,000
Celgene [Member] | Participation Service [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recognition, selling price																200,000
Celgene [Member] | MTD [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Received amount of development cost													5,000,000
Celgene [Member] | Before Amendment [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of years company expected to fulfill its performance obligations													6 years
Collaboration revenue													65,400,000	25,500,000	25,100,000
Maximum [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Discovery phase years														5 years
Milestone payment upon achievement of a specified clinical development milestone event					25,000,000								25,000,000
Receipts of potential milestone payments					120,000,000								120,000,000
Milestone payments upon achievement of specified regulatory milestone events					70,000,000								70,000,000
Milestone payment upon achievement of a specified commercial milestone event					25,000,000								25,000,000
Maximum [Member] | Celgene [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payment upon achievement of a specified clinical development milestone event					10,000,000								10,000,000
Series B Convertible Preferred Stock [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Series B convertible preferred stock, purchased				5,190,551
Series B convertible preferred stock price per share					$ 1.70								$ 1.70
Net proceeds of Series B convertible preferred stock													8,800,000
Additional consideration under agreement													3,100,000
Series B convertible preferred stock at fair value					$ 5,700,000								$ 5,700,000
Reverse stock split													1-for-2.75
Reverse stock split ratio													0.3636
Additional outstanding shares common stock														(5,190,551)					1,887,473
Series B Convertible Preferred Stock [Member] | Celgene [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Series B convertible preferred stock, purchased					5,190,551								5,190,551