Selected Quarterly Financial Data - Quarterly Financial Data (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Statement [Abstract]
Product sales	$ 7,460	$ 6,096	$ 5,802	$ 5,795	$ 8,040	$ 14,672	$ 10,324	$ 11,810	$ 25,152	$ 44,846	$ 35,399
Total revenue	19,551	132,871	28,513	19,771	31,146	60,909	33,862	23,004	200,707	148,921	81,191
Cost of goods sold	6,298	9,220	5,108	7,907	8,960	12,877	5,011	11,661	28,533	38,509	30,428
Research and development expenses	38,494	34,200	36,702	38,338	48,248	43,914	52,230	45,618	147,734	190,010	148,675
Operating income (loss)	(37,488)	80,321	(22,916)	(36,402)	(35,894)	(6,525)	(32,605)	(45,106)	(16,485)	(120,130)	(141,201)
Net income (loss)	$ (45,683)	$ 70,605	$ (32,637)	$ (46,201)	$ (47,659)	$ (16,543)	$ (42,748)	$ (55,063)	$ (53,916)	$ (162,013)	$ (171,855)
Net income (loss) per share
Basic	$ (0.35)	$ 0.55	$ (0.26)	$ (0.37)	$ (0.41)	$ (0.14)	$ (0.37)	$ (0.48)
Diluted	$ (0.35)	$ 0.53	$ (0.26)	$ (0.37)	$ (0.41)	$ (0.14)	$ (0.37)	$ (0.48)