Condensed Consolidated Statements of Operations and Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Income Statement [Abstract]
Collaboration revenue	$ 1,091	$ 0
Operating expenses:
Research and development	4,878	10,350
General and administrative	1,778	2,345
Total operating expenses	6,656	12,695
Loss from operations	(5,565)	(12,695)
Other income (expense):
Interest expense	(120)	(70)
Interest income	152	384
Net loss	(5,533)	(12,381)
Comprehensive income (loss):
Unrealized (loss) gain on investments	(15)	15
Unrealized loss on foreign currency translation	(113)	(14)
Comprehensive loss	$ (5,661)	$ (12,380)
Weighted-average shares used to compute basic and diluted net loss per share (in shares)	18,587,892	17,671,918
Basic and diluted net loss per share (in dollars per share)	$ (0.30)	$ (0.70)