CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating expenses:
Research and development	$ 33,476	$ 15,339	$ 6,507
General and administrative	15,091	5,328	2,026
Total operating expenses	48,567	20,667	8,533
Loss from operations	(48,567)	(20,667)	(8,533)
Other income, net	488	104	16
Net loss	(48,079)	(20,563)	(8,517)
Accretion of convertible preferred stock		(2,566)	(2,054)
Net loss attributable to common stockholders	$ (48,079)	$ (23,129)	$ (10,571)
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)	$ (2.25)	$ (3.79)	$ (6.15)
Weighted average common shares outstanding, basic and diluted (in shares)	21,415,733	6,107,042	1,720,082
Other comprehensive loss:
Unrealized gain (loss) on marketable securities, net of tax of $0	$ 105	$ (148)	$ (9)
Foreign currency translation adjustments	(225)	5
Total other comprehensive loss	(120)	(143)	(9)
Comprehensive loss	$ (48,199)	$ (20,706)	$ (8,526)