CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Statement Of Income And Comprehensive Income [Abstract]
Collaboration revenue	$ 3,318	$ 3,423	$ 17,821	$ 8,176
Operating expenses:
Research and development, net	7,053	3,969	21,646	12,135
General and administrative	3,881	3,810	10,871	17,141
Total operating expenses	10,934	7,779	32,517	29,276
Loss from operations	(7,616)	(4,356)	(14,696)	(21,100)
Gain (loss) from equity-method investment	303	(47)	15	(47)
Finance (expense) income, net	(120)	150	(321)	373
Net loss	$ (7,433)	$ (4,253)	$ (15,002)	$ (20,774)
Net loss per share, basic and diluted	$ (0.56)	$ (0.42)	$ (1.18)	$ (2.07)
Weighted-average shares outstanding, basic and diluted	13,201	10,093	12,734	10,059
Comprehensive loss:
Net loss	$ (7,433)	$ (4,253)	$ (15,002)	$ (20,774)
Unrealized gain on short-term investments		2		7
Comprehensive loss	$ (7,433)	$ (4,251)	$ (15,002)	$ (20,767)