Collaboration Agreement - Schedule of Collaboration Revenue Related to U.S. XTANDI Net Sales (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue related to U.S. XTANDI net sales	$ 156,501	$ 90,723	$ 417,731	$ 224,814
U.S. XTANDI sales [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue related to U.S. XTANDI net sales	156,501	90,723	417,731	224,814
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)	313,003	181,446	835,463	449,629
Shared U.S. development and commercialization costs	(85,384)	(69,616)	(280,644)	(217,866)
Pre-tax U.S. profit	227,619	111,830	554,819	231,763
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	113,809	55,915	277,409	115,881
Reimbursement of Medivation's share of shared U.S. costs	$ 42,692	$ 34,808	$ 140,322	$ 108,933