Collaboration Agreement - Schedule of Collaboration Revenue Related to U.S. XTANDI Net Sales (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue related to U.S. XTANDI net sales	$ 112,010	$ 62,225
U.S. XTANDI sales [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue related to U.S. XTANDI net sales	112,010	62,225
U.S. XTANDI sales [Member] | Astellas Pharma Inc. [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
U.S. XTANDI net sales (as reported by Astellas)	224,020	124,451
Shared U.S. development and commercialization costs	(110,313)	(77,707)
Pre-tax U.S. profit	113,707	46,744
U.S. XTANDI sales [Member] | Medivation [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Medivation's share of pre-tax U.S. profit	56,853	23,372
Reimbursement of Medivation's share of shared U.S. costs	$ 55,157	$ 38,853