Collaboration Agreements - Additional Information (Detail) (USD $)	1 Months Ended	3 Months Ended		12 Months Ended		1 Months Ended	0 Months Ended
	Apr. 30, 2010	Mar. 31, 2015 Candidate	Mar. 31, 2014	Dec. 31, 2014	Dec. 31, 2013	Jul. 31, 2014	Jul. 31, 2014
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Agreement amended date	2011-10
Amended collaboration expiration date	2014-04			2016-04	2015-04
Discovery phase years	2 years
Term of the initial discovery period before amendment to extend				5 years	4 years
Term of extended period after amendment of the initial discovery period				6 years	5 years
Eligible payment to be received from extension of the discovery phase				$ 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
Payment made in pursuant to the amendment				20,000,000
Recognized revenue to extension		0
Increase in revenue		34,202,000	8,411,000
Achievement of an early clinical development milestone event		22,500,000
Dosing of the last patient in a Company-sponsored		25,000,000
Development cost reimbursed		33,100,000
Collaboration receivable		7,000,000		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
Milestone payment reimbursement, percentage		50.00%				50.00%
Reduction in research and development expenditure		(3,800,000)
Increase in revenue		5,100,000
Reduction in net loss		8,900,000
Decrease in net loss per share		$ 0.24
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
Revenue recognized		15,800,000
Celgene [Member] | In Process Research and Development [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recognition, selling price							13,600,000
Celgene [Member] | Participation Service [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recognition, selling price							200,000
Celgene [Member] | Planning Services [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Reduction in research and development expenditure		600,000
Revenue		100,000
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
Phase 1 [Member] | Celgene [Member] | In Process Research and Development [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recognition, selling price							50,800,000
Maximum [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payment upon achievement of a specified clinical development milestone event		25,000,000
Receipts of potential milestone payments		120,000,000
Milestone payments upon achievement of specified regulatory milestone events		70,000,000
Milestone payment upon achievement of a specified commercial milestone event		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