CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Revenue:
Total revenue	$ 4,461	$ 8,386
Operating expenses:
Research and development	34,794	30,421
General and administrative	11,646	11,049
Total operating expenses	46,440	41,470
Loss from operations	(41,979)	(33,084)
Other income (expense):
Interest and other income	941	1,254
Interest and other expense	(835)	(873)
Net loss	(41,873)	(32,703)
Change in unrealized gain (loss) on investments	3	(3)
Comprehensive loss	(41,870)	(32,706)
Net loss	$ (41,873)	$ (32,703)
Net loss per share, basic and diluted (in dollars per share)	$ (1.34)	$ (1.10)
Weighted-average shares used to compute basic and diluted net loss per share (in shares)	31,336,409	29,600,332
Collaboration revenue
Revenue:
Total revenue	$ 4,308	$ 7,373
Grant revenue
Revenue:
Total revenue	$ 153	$ 1,013