Description of Business - Additional Information (Detail) (USD $)	3 Months Ended	31 Months Ended
	Mar. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Organization And Description Of Business [Line Items]
Cumulative net losses	$ (60,827,000)	$ (60,827,000)	$ (57,709,000)
Debt instrument, interest rate	2.625%	2.625%
Convertible 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 products	1	1
XTANDI [Member] | Astellas Pharma Inc. [Member]
Organization And Description Of Business [Line Items]
World wide net sales		$ 1,900,000,000
Collaborative agreement [Member] | Astellas Pharma Inc. [Member]
Organization And Description Of Business [Line Items]
Range of percentage rates for royalties received on ex-U.S. net sales, as defined by collaboration agreement	Low teens to the low twenties