Collaboration Agreement - Schedule of Collaboration Revenue Related to U.S. XTANDI Sales (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue related to U.S. XTANDI sales	$ 90,723	$ 54,244	$ 224,814	$ 133,134
U.S. XTANDI sales [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue related to U.S. XTANDI sales	90,723	54,244	224,814	133,134
U.S. XTANDI sales [Member] | Astellas Pharma Inc. [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
U.S. XTANDI sales (as reported by Astellas)	181,446	108,487	449,629	266,267
Shared U.S. development and commercialization costs	(69,616)	(58,901)	(217,866)	(178,002)
Pre-tax U.S. profit	111,830	49,586	231,763	88,265
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	55,915	24,793	115,881	44,133
Reimbursement of Medivation's share of shared U.S. costs	$ 34,808	$ 29,451	$ 108,933	$ 89,001