Description of Business - Additional Information (Detail) (USD $)	12 Months Ended	28 Months Ended
	Dec. 31, 2014	Dec. 31, 2014	Dec. 31, 2013
Organization And Description Of Business [Line Items]
Cumulative net losses	$ (57,709,000)	$ (57,709,000)	$ (334,161,000)
Debt instrument, interest rate	2.625%	2.625%
Convertible senior notes, maturity date	Apr. 01, 2017
Astellas Pharma Inc. [Member] | Milestone and cost-sharing payments [Member]
Organization And Description Of Business [Line Items]
Remaining sales milestone payments may receive	245,000,000
XTANDI [Member]
Organization And Description Of Business [Line Items]
Number of commercial product	1	1
XTANDI [Member] | Astellas Pharma Inc. [Member]
Organization And Description Of Business [Line Items]
World wide net sales		$ 1,600,000,000
Collaborative agreement [Member] | Astellas Pharma Inc. [Member]
Organization And Description Of Business [Line Items]
Royalty received on ex-U.S. sales per collaboration arrangement	Low teens to the low twenties