Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenues:
Grant	$ 4,628	$ 6,085	$ 0
Operating expenses:
Research and development	18,143	11,453	6,830
General and administrative	8,391	5,947	2,074
Total operating expenses	26,534	17,400	8,904
Loss from operations	(21,906)	(11,315)	(8,904)
Other income (expense):
Interest income	244	22	1
Change in fair value of forward sale contract			(1,444)
Other expense, net	(36)	(2)
Total other income (expense)	208	20	(1,443)
Net loss	(21,698)	(11,295)	(10,347)
Deemed dividend to convertible preferred stockholders		(228)
Net loss attributable to common shareholders and stockholders	$ (21,698)	$ (11,523)	$ (10,347)
Common Stock
Other income (expense):
Basic and diluted net loss per share	$ (2.22)	$ (19.21)
Net loss attributable to common shareholders and stockholders	$ (21,698)	$ (11,523)
Basic and diluted weighted-average shares outstanding	9,791,728	599,788
Class A-1 Common
Other income (expense):
Basic and diluted net loss per share			$ (20.13)
Net loss attributable to common shareholders and stockholders			$ (3,321)
Basic and diluted weighted-average shares outstanding			165,000
Class A Common
Other income (expense):
Basic and diluted net loss per share			$ (17.06)
Net loss attributable to common shareholders and stockholders			$ (5,706)
Basic and diluted weighted-average shares outstanding			334,522
Class B Common
Other income (expense):
Basic and diluted net loss per share			$ (40.17)
Net loss attributable to common shareholders and stockholders			$ (1,320)
Basic and diluted weighted-average shares outstanding			32,861