Condensed Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Income Statement [Abstract]
License revenue	$ 38	$ 38
Research and development:
Noncash compensation	1,489	2,859
Other research and development	30,896	32,159
Total research and development	32,385	35,018
General and administrative:
Noncash compensation	393	4,478
Other general and administrative	1,949	2,119
Total general and administrative	2,342	6,597
Total costs and expenses	34,727	41,615
Operating loss	(34,689)	(41,577)
Other (income) expense:
Interest income	(149)	(144)
Other expense	616	96
Total other (income) expense, net	467	(48)
Net loss	$ (35,156)	$ (41,529)
Basic and diluted net loss per common share	$ (0.43)	$ (0.59)
Weighted average shares used in computing basic and diluted net loss per common share	81,174,301	70,636,970