Collaboration Agreements - Additional Information (Detail) - USD ($)	1 Months Ended		7 Months Ended	12 Months Ended			34 Months Ended
	Feb. 29, 2016	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2016
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Amount of certain milestones achieved in account receivable			$ 19,725,000	$ 22,193,000	$ 19,725,000		$ 22,193,000
Revenue recognized under collaboration agreement				17,355,000	6,028,000	$ 3,096,000
Estimated deferred revenue recognized within one year			5,261,000	19,033,000	5,261,000		19,033,000
Celgene Corporation | Collaborative Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments		$ 17,000,000
Amount of certain milestones achieved in account receivable						6,000,000
Revenue recognized under collaboration agreement				3,200,000	2,200,000	2,900,000
Deferred revenue recorded under collaboration agreement				5,500,000			5,500,000
Estimated deferred revenue recognized within one year				$ 1,200,000			1,200,000
Collaborative agreement period				1 year
Celgene Corporation | Collaborative Arrangement | Upfront Payment Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration agreement upfront payment		5,800,000					2,100,000
Celgene Corporation | Collaborative Arrangement | Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments		$ 45,000,000
Merck Sharp & Dohme Corp. | Collaborative Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred revenue recorded under collaboration agreement				$ 21,400,000			21,400,000
Collaborative agreement period				1 year
Merck Sharp & Dohme Corp. | Collaborative Arrangement | Upfront Payment Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration agreement upfront payment	$ 12,000,000			$ 8,500,000
Merck Sharp & Dohme Corp. | Collaborative Arrangement | Development Funding
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration agreement upfront payment			$ 3,900,000	9,600,000
Merck Sharp & Dohme Corp. | Clinical Collaborative Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recognized under collaboration agreement				8,600,000	3,700,000	0
Estimated deferred revenue recognized within one year				10,100,000			10,100,000
Merck Sharp & Dohme Corp. | New Clinical Collaborative Arrangement | Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments	$ 12,000,000.0
Medivation, Inc. and Astellas Pharma, Inc. | Collaborative Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration agreement upfront payment				2,900,000
Revenue recognized under collaboration agreement				4,800,000	$ 0	$ 0
Deferred revenue recorded under collaboration agreement				$ 10,000,000			10,000,000
Collaborative agreement period				1 year
Medivation, Inc. and Astellas Pharma, Inc. | Collaborative Arrangement | Upfront Payment Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration agreement upfront payment				$ 6,000,000
Medivation, Inc. and Astellas Pharma, Inc. | Clinical Collaborative Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Estimated deferred revenue recognized within one year				4,000,000			$ 4,000,000
Medivation, Inc. and Astellas Pharma, Inc. | Clinical Collaborative Arrangement | Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments				6,000,000
Medivation, Inc. and Astellas Pharma, Inc. | Development Funding | Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments				$ 10,000,000