Unaudited Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Operating expenses:
Research and development	$ 10,009	$ 8,516	$ 17,694	$ 16,202
General and administrative	5,198	6,332	10,679	11,977
Total operating expenses	15,207	14,848	28,373	28,179
Loss from operations	(15,207)	(14,848)	(28,373)	(28,179)
Interest income	617	602	1,287	1,075
Other income (expense)	151	0	151	(16)
Loss before income tax provision (benefit)	(14,439)	(14,246)	(26,935)	(27,120)
Income tax provision (benefit)	4	(1,037)	9	(838)
Net loss	(14,443)	(13,209)	(26,944)	(26,282)
Comprehensive loss	$ (14,443)	$ (13,209)	$ (26,944)	$ (26,282)
Net loss per common share:
Net loss per common shares - basic and diluted (in dollars per share)	$ (0.35)	$ (0.37)	$ (0.65)	$ (0.73)
Weighted average common shares outstanding:
Weighted average common shares outstanding - basic and dilutive (in shares)	41,477	36,188	41,452	36,171