Condensed Consolidated Statements of Operations (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Operating expenses:
Research and development	$ 12,007	$ 5,696	$ 23,289	$ 11,321
General and administrative	3,124	1,395	6,115	2,810
Total operating expenses	15,131	7,091	29,404	14,131
Loss from operations	(15,131)	(7,091)	(29,404)	(14,131)
Interest income	152	27	324	39
Change in fair value of redeemable convertible preferred stock tranche and warrant liabilities	0	0	0	(4,719)
Other expense	0	(34)	0	(34)
Net loss	(14,979)	(7,098)	(29,080)	(18,845)
Net loss attributable to common stockholders	$ (14,979)	$ (7,323)	$ (29,080)	$ (19,110)
Net loss per share attributable to common stockholders, basic and diluted (in usd per share)	$ (0.89)	$ (19.07)	$ (1.73)	$ (56.90)
Weighted-average shares used to compute net loss per share attributable to common stockholders, basic and diluted	16,875,627	383,910	16,821,225	335,855