Selected Quarterly Financial Data - Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Statement [Abstract]
Product sales	$ 13,690	$ 14,698	$ 12,867	$ 14,099	$ 13,973	$ 7,240	$ 10,968	$ 7,974	$ 55,354	$ 40,155	$ 25,152
Total revenue	37,450	36,336	32,768	58,882	39,370	59,952	22,661	108,801	165,436	230,784	200,707
Cost of goods sold	6,604	7,033	7,708	8,870	8,364	6,760	10,534	8,444	30,215	34,102	28,533
Research and development expenses	50,232	51,951	52,350	49,268	47,135	43,229	45,412	47,011	203,801	182,787	147,734
Operating income (loss)	(32,145)	(32,901)	(38,325)	(9,484)	(29,364)	419	(43,469)	43,043	(112,855)	(29,371)	(16,485)
Net income (loss)	$ (42,199)	$ (43,224)	$ (48,603)	$ (19,498)	$ (54,137)	$ (8,203)	$ (52,657)	$ 33,820	$ (153,524)	$ (81,177)	$ (53,916)
Net income (loss) per share
Basic	$ (0.28)	$ (0.32)	$ (0.36)	$ (0.14)	$ (0.40)	$ (0.06)	$ (0.40)	$ 0.26
Diluted	$ (0.28)	$ (0.32)	$ (0.36)	$ (0.14)	$ (0.40)	$ (0.06)	$ (0.40)	$ 0.25