Collaboration Agreement - Schedule of Collaboration Revenue Attributable to Sales (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue attributable to U.S. XTANDI sales	$ 62,225	$ 37,689
U.S. XTANDI sales [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue attributable to U.S. XTANDI sales	62,225	37,689
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)	124,451	75,378
Shared U.S. development and commercialization costs	(77,707)	(57,670)
Pre-tax U.S. profit	46,744	17,708
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	23,372	8,854
Reimbursement of Medivation's share of shared U.S. costs	$ 38,853	$ 28,835