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
Operating expenses:
Research and development	$ 8,660	$ 9,834	$ 18,817	$ 19,462
General and administrative	4,257	2,715	8,592	5,774
Total operating expenses	12,917	12,549	27,409	25,236
Loss from operations	(12,917)	(12,549)	(27,409)	(25,236)
Other income (expense):
Interest income	161	169	331	266
Other income (expense), net	74	(27)	8	(39)
Total other income	235	142	339	227
Net loss	$ (12,682)	$ (12,407)	$ (27,070)	$ (25,009)
Net loss per share, basic and diluted (in USD per share)	$ (0.30)	$ (0.29)	$ (0.64)	$ (0.67)
Weighted-average common shares outstanding, basic and diluted (in shares)	42,368,973	42,207,376	42,368,919	37,452,655