Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
Collaboration revenue	$ 0	$ 209,977	$ 50,909
Operating expenses:
Research and development	41,737	66,289	196,295
General and administrative	23,612	35,683	50,178
Total operating expenses	65,349	101,972	246,473
Income (loss) from operations	(65,349)	108,005	(195,564)
Interest income	2,389	1,522	1,704
Gain on extinguishment of Royalty Purchase Liability	125,000	0	0
Other income (expense)	(16)	(34)	34
Income (loss) before income tax benefit	62,024	109,493	(193,826)
Income tax benefit	(1,063)	(4,712)	(406)
Net income (loss)	$ 63,087	$ 114,205	$ (193,420)
Net income (loss) per common share:
Basic (in dollars per share)	$ 1.70	$ 3.18	$ (5.45)
Dilutive (in dollars per share)	$ 1.70	$ 3.17	$ (5.45)
Weighted average common shares outstanding:
Basic (in shares)	37,061	35,919	35,486
Dilutive (in shares)	37,088	36,007	35,486