Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating expenses:
Research and development	$ 39,341	$ 30,046	$ 39,773
General and administrative	13,314	11,220	12,347
Total operating expenses	52,655	41,266	52,120
Loss from operations	(52,655)	(41,266)	(52,120)
Other income:
Interest income	650	284	58
Other income (expense), net	(73)	13	39
Total other income	577	297	97
Net loss	$ (52,078)	$ (40,969)	$ (52,023)
Net loss per share, basic and diluted (usd per share)	$ (1.31)	$ (1.31)	$ (2.07)
Weighted-average common shares outstanding, basic and diluted (in shares)	39,859,009	31,387,579	25,152,948