Condensed Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income Statement [Abstract]
License revenue	$ 38	$ 38	$ 76	$ 76
Research and development:
Non-cash stock expense associated with in-licensing agreements	3,000	0	4,000	0
Noncash compensation	888	1,266	3,747	3,573
Other research and development	34,812	25,440	65,971	45,815
Total research and development	38,700	26,706	73,718	49,388
General and administrative:
Noncash compensation	3,375	223	7,854	3,913
Other general and administrative	2,308	1,534	4,426	2,867
Total general and administrative	5,683	1,757	12,280	6,780
Total costs and expenses	44,383	28,463	85,998	56,168
Operating loss	(44,345)	(28,425)	(85,922)	(56,092)
Other (income) expense:
Interest income	(189)	(50)	(333)	(95)
Other (income) expense	(14)	(22)	82	84
Total other income, net	(203)	(72)	(251)	(11)
Net loss	$ (44,142)	$ (28,353)	$ (85,671)	$ (56,081)
Basic and diluted net loss per common share	$ (0.59)	$ (0.45)	$ (1.18)	$ (0.96)
Weighted average shares used in computing basic and diluted net loss per common share	74,256,348	63,288,269	72,456,657	58,251,045