CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Revenue:
Total revenue	$ 8,386	$ 4,003
Operating expenses:
Research and development	30,421	19,623
General and administrative	11,049	10,912
Total operating expenses	41,470	30,535
Loss from operations	(33,084)	(26,532)
Other income (expense):
Interest and other income	1,254	403
Interest and other expense	(873)	(383)
Net loss	(32,703)	(26,512)
Change in unrealized loss on investments	(3)	0
Comprehensive loss	(32,706)	(26,512)
Accretion of redeemable convertible preferred stock to redemption value	0	(5)
Net loss available to common stockholders	$ (32,703)	$ (26,517)
Net loss per share, basic and diluted (in dollars per share)	$ (1.10)	$ (1.38)
Weighted-average shares used to compute basic and diluted net loss per share (in shares)	29,600,332	19,244,605
Collaboration revenue
Revenue:
Total revenue	$ 7,373	$ 3,097
Grant revenue
Revenue:
Total revenue	$ 1,013	$ 906