Financial Information by Quarter (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues:
Product, net	$ 57,277	$ 45,954	$ 35,011	$ 16,342	$ 5,421				$ 154,584	$ 5,421
Total revenues	57,277	45,954	35,011	16,342	5,421				154,584	5,421	$ 1,253
Cost and operating expenses:
Cost of sales (excluding amortization of in-licensed rights)	3,546	3,078	505	224	101				7,353	101
Research and development	44,441	34,239	58,908	29,119	70,749	$ 34,349	$ 44,348	$ 38,826	166,707	188,272	146,394
Selling, general and administrative	32,221	28,176	36,069	26,216	22,937	22,184	17,752	20,876	122,682	83,749	75,043
Settlement and license charges		25,588	2,839						28,427
Amortization of in-licensed rights	216	780	29	28	29				1,053	29
Total cost and expenses	80,424	91,861	98,350	55,587	93,816	56,533	62,100	59,702	326,222	272,151	221,437
Operating loss	(23,147)	(45,907)	(63,339)	(39,245)	(88,395)	(56,533)	(62,100)	(59,702)	(171,638)	(266,730)	(220,184)
Other (loss) income:
Interest (expense) income and other, net	(2,693)	184	184	335	(57)	(209)	(201)	(68)	(1,990)	(535)	154
Gain from sale of Priority Review Voucher				125,000					125,000
Total other income (loss)	(2,693)	184	184	125,335	(57)	(209)	(201)	(68)	123,010	(535)	154
Loss before income tax expense	(25,840)	(45,723)	(63,155)	86,090					(48,628)	(267,265)	(220,030)
Income tax (benefit) expense	(1,842)	2,011	(109)	2,000					2,060
Net loss	$ (23,998)	$ (47,734)	$ (63,046)	$ 84,090	$ (88,452)	$ (56,742)	$ (62,301)	$ (59,770)	$ (50,688)	$ (267,265)	$ (220,030)
Net income (loss) per share:
Basic (loss) earnings per share	$ (0.37)	$ (0.78)	$ (1.15)	$ 1.53
Diluted (loss) earnings per share	$ (0.37)	$ (0.78)	$ (1.15)	$ 1.50
Weighted average number of shares of common stock used in calculating:
Weighted-average number of shares of common stock outstanding for computing basic loss per share	64,277	61,528	54,976	54,850					58,818	48,697	42,290
Diluted (loss) earnings per share	64,277	61,258	54,976	56,012
Net loss per share — basic and diluted					$ (1.62)	$ (1.18)	$ (1.35)	$ (1.31)	$ (0.86)	$ (5.49)	$ (5.20)
Shares used in per share calculations—basic and diluted					54,619	48,254	46,157	45,697	58,818	48,697	42,290