Collaboration Agreement - Schedule of Collaboration Revenue Related to U.S. XTANDI Net Sales (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue related to U.S. XTANDI net sales	$ 149,220	$ 71,866	$ 261,230	$ 134,091
U.S. XTANDI sales [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue related to U.S. XTANDI net sales	149,220	71,866	261,230	134,091
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)	298,440	143,732	522,460	268,183
Shared U.S. development and commercialization costs	(84,947)	(70,543)	(195,260)	(148,250)
Pre-tax U.S. profit	213,493	73,189	327,200	119,933
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	106,747	36,594	163,600	59,966
Reimbursement of Medivation's share of shared U.S. costs	$ 42,473	$ 35,272	$ 97,630	$ 74,125