Collaboration Agreements - Additional Information (Detail) - USD ($)	1 Months Ended					3 Months Ended		6 Months Ended		12 Months Ended
	Feb. 29, 2016	Jan. 31, 2016	Dec. 31, 2015	Jul. 31, 2015	Mar. 31, 2014	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015	Dec. 31, 2014
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration agreement upfront payment			$ 1,600,000
Minimum annual revenue period								3 years
Amount of certain milestones achieved in account receivable			19,725,000			$ 25,238,000		$ 25,238,000		$ 19,725,000
Revenue recognized under collaboration agreement						5,139,000	$ 568,000	7,700,000	$ 1,329,000
Estimated deferred revenue recognized within one year			$ 5,261,000			16,873,000		16,873,000		5,261,000
Celgene Corporation | Collaborative Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Maximum success-based milestone payments					$ 45,000,000.0
Amount of certain milestones achieved in account receivable											$ 6,000,000
Revenue recognized under collaboration agreement						900,000	300,000	1,700,000	1,000,000
Deferred revenue recorded under collaboration agreement						6,700,000		6,700,000
Estimated deferred revenue recognized within one year						2,100,000		2,100,000
Celgene Corporation | Upfront Payment Arrangement | Collaborative Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration agreement upfront payment					$ 5,800,000
Celgene Corporation | Maximum | Collaborative Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Maximum success-based milestone payments								17,000,000.0
Merck Sharp & Dohme Corp. | Collaborative Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred revenue recorded under collaboration agreement						22,500,000		22,500,000
Merck Sharp & Dohme Corp. | Clinical Research Collaborative Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recognized under collaboration agreement						2,600,000	200,000	3,900,000	200,000
Deferred revenue recorded under collaboration agreement						7,700,000		$ 7,700,000
Collaborative agreement period								1 year
Merck Sharp & Dohme Corp. | Upfront Payment Arrangement | Collaborative Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration agreement upfront payment	$ 12,000,000			$ 2,000,000		8,500,000				$ 1,900,000
Merck Sharp & Dohme Corp. | Maximum | Clinical Research Collaborative Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Maximum success-based milestone payments	$ 12,000,000.0							$ 4,000,000.0
Medivation, Inc. and Astellas Pharma, Inc. | Collaborative Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recognized under collaboration agreement						1,500,000	$ 0	2,100,000	$ 0
Deferred revenue recorded under collaboration agreement						10,800,000		10,800,000
Medivation, Inc. and Astellas Pharma, Inc. | Clinical Research Collaborative Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred revenue recorded under collaboration agreement						$ 4,200,000		$ 4,200,000
Medivation, Inc. and Astellas Pharma, Inc. | Upfront Payment Arrangement | Collaborative Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration agreement upfront payment		$ 6,000,000
Medivation, Inc. and Astellas Pharma, Inc. | Maximum | Clinical Research Collaborative Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Maximum success-based milestone payments		6,000,000.0
Medivation, Inc. and Astellas Pharma, Inc. | Maximum | Development Funding
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Maximum success-based milestone payments		$ 10,000,000.0