Quarterly Financial Information (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended														6 Months Ended		12 Months Ended
	Dec. 31, 2016	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, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2016	Jun. 30, 2015
Revenues:
License and milestone fees		$ 29,580	$ 79	$ 31,080	$ 18,730	$ 5,076	$ 76	$ 76	$ 10,077	$ 10,692	$ 6,070	$ 5,086	$ 5,078	$ 41,417	$ 6,234	$ 5,152	$ 16,762	$ 79,469	$ 15,305	$ 26,915	$ 57,815
Royalty revenue										195			5,099	4,625	4,166		195			195	13,867
Royalty revenue (reversed)												(23)
Non-cash royalty revenue related to the sale of future royalties		7,587	6,503	6,439	7,613	6,710	6,184	5,944	7,380	6,291	5,684	5,484				12,894	11,975	28,142	26,218	25,299	5,484
Research and development support		452	650	902	1,478	1,427	1,354	1,335	1,059	848	772	708	532	832	776	2,781	1,620	3,482	5,175	4,014	2,848
Clinical materials revenue		1,829	1,248	599	678	633	46	53	1,198	3	2,325	1,356	718	1,426	2,027	679	2,328	4,354	1,930	3,579	5,527
Total revenues		39,448	8,480	39,020	28,499	13,846	7,660	7,408	19,714	18,029	14,851	12,611	11,427	48,300	13,203	21,506	32,880	115,447	48,628	60,002	85,541
Expenses:
Research and development		39,843	31,689	35,319	32,888	33,657	32,909	38,652	36,094	38,199	35,132	30,437	25,666	27,647	28,018	66,566	73,331	139,739	141,312	148,077	111,768
General and administrative		9,048	7,908	8,836	8,119	8,536	9,459	9,298	11,235	8,054	8,329	7,261	7,000	6,872	7,095	17,995	16,383	33,911	38,528	36,916	28,228
Restructuring charge	$ 273	393			386	301	4,130									4,431		779	4,431
Total operating expenses		49,284	39,597	44,155	41,393	42,494	46,498	47,950	47,329	46,253	43,461	37,698	32,666	34,519	35,113	88,992	89,714	174,429	184,271	184,993	139,996
Loss from operations		(9,836)	(31,117)	(5,135)	(12,894)	(28,648)	(38,838)	(40,542)	(27,615)	(28,224)	(28,610)	(25,087)	(21,239)	13,781	(21,910)	(67,486)	(56,834)	(58,982)	(135,643)	(124,991)	(54,455)
Non-cash interest expense on liability related to the sale of future royalties and convertible senior notes		(3,221)	(3,385)	(3,501)	(3,575)	(3,647)	(5,018)	(4,956)	(4,972)	(5,059)	(5,143)	(5,437)				(8,665)	(10,202)	(13,682)	(18,593)	(20,130)	(5,437)
Interest expense on convertible senior notes		(28)	(762)	(1,125)	(1,125)	(1,099)	(1,150)									(2,249)		(3,040)	(2,387)	(138)
Non-cash debt conversion expense		(724)	(22,191)															(22,915)
Other (expense) income, net		691	773	894	249	(758)	275	(424)	659	56	13	50	(379)	(146)	(372)
Net loss		$ (13,118)	$ (56,682)	$ (8,867)	$ (17,345)	$ (34,152)	$ (44,731)	$ (45,922)	$ (31,928)	$ (33,227)	$ (33,740)	$ (30,474)	$ (21,618)	$ 13,635	$ (22,282)	$ (78,883)	$ (66,967)	$ (96,012)	$ (156,733)	$ (144,817)	$ (60,739)
Basic and diluted net (loss) income per common share (in dollars per share)		$ (0.11)	$ (0.61)	$ (0.10)	$ (0.20)	$ (0.39)	$ (0.51)	$ (0.53)	$ (0.37)	$ (0.38)	$ (0.39)	$ (0.35)	$ (0.25)	$ 0.16	$ (0.26)	$ (0.91)	$ (0.77)	$ (0.98)	$ (1.80)	$ (1.67)	$ (0.71)