Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement Of Income And Comprehensive Income [Abstract]
Government research contracts and grants revenue			$ 112
Operating expenses:
Research and development	$ 46,489	$ 16,569	6,770
General and administrative	13,337	9,265	5,170
Total operating expenses	59,826	25,834	11,940
Operating loss	(59,826)	(25,834)	(11,828)
Other income (expense):
Interest income	81	48	58
Interest expense	(2)	(1)	(701)
Change in the fair value of the warrant liability			(641)
Other income, net	48	1	9
Total other income (expense)	127	48	(1,275)
Loss from continuing operations	(59,699)	(25,786)	(13,103)
Income (loss) from discontinued operations		(2,274)	1,715
Net loss and comprehensive loss	$ (59,699)	$ (28,060)	$ (11,388)
Income (loss) per share, basic and diluted:
Continuing operations	$ (9.97)	$ (11.36)	$ (5.95)
Discontinued operations		(1.01)	0.78
Net loss per share, basic and diluted	$ (9.97)	$ (12.37)	$ (5.17)
Weighted-average common shares outstanding, basic and diluted	5,985,985	2,269,124	2,203,278