Collaboration Agreement - Schedule of Collaboration Revenue Related to U.S. XTANDI Sales (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue related to U.S. XTANDI sales	$ 71,866	$ 41,201	$ 134,091	$ 78,890
U.S. XTANDI sales [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue related to U.S. XTANDI sales	71,866	41,201	134,091	78,890
U.S. XTANDI sales [Member] | Astellas Pharma Inc. [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Net U.S. sales (as reported by Astellas)	143,732	82,402	268,183	157,780
Shared U.S. development and commercialization costs	(70,543)	(61,431)	(148,250)	(119,101)
Pre-tax U.S. profit	73,189	20,971	119,933	38,679
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	36,594	10,486	59,966	19,340
Reimbursement of Medivation's share of shared U.S. costs	$ 35,272	$ 30,715	$ 74,125	$ 59,550