Financial Information by Quarter (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ 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
Revenues:
Product, net	$ 5,421								$ 5,421
Revenue from research contracts and other grants					$ 1,253					$ 1,253	$ 9,757
Total revenues	5,421								5,421	1,253	9,757
Operating expenses:
Cost of sales	130								130
Research and development	70,749	$ 34,349	$ 44,348	$ 38,826	41,376	$ 36,673	$ 29,180	$ 39,165	188,272	146,394	94,231
Selling, general and administrative	22,937	22,184	17,752	20,876	24,329	15,090	12,927	22,697	83,749	75,043	49,315
Total cost and expenses	93,816	56,533	62,100	59,702	65,705	51,763	42,107	61,862	272,151	221,437	143,546
Operating loss	(88,395)	(56,533)	(62,100)	(59,702)	(64,452)	(51,763)	(42,107)	(61,862)	(266,730)	(220,184)	(133,789)
Other (loss) income:
Interest (expense) income and other, net	(57)	(209)	(201)	(68)	(229)	(176)	256	303	(535)	154	779
Total other (loss) income	(57)	(209)	(201)	(68)	(229)	(176)	256	303	(535)	154	(2,000)
Net loss	$ (88,452)	$ (56,742)	$ (62,301)	$ (59,770)	$ (64,681)	$ (51,939)	$ (41,851)	$ (61,559)	$ (267,265)	$ (220,030)	$ (135,789)
Net loss per share — basic and diluted	$ (1.62)	$ (1.18)	$ (1.35)	$ (1.31)	$ (1.44)	$ (1.25)	$ (1.01)	$ (1.49)	$ (5.49)	$ (5.20)	$ (3.39)
Shares used in per share calculations—basic and diluted	54,619	48,254	46,157	45,697	44,882	41,565	41,357	41,324	48,697	42,290	40,026