Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Condensed Consolidated Statements of Operations and Comprehensive Loss
Collaboration revenues	$ 1,522	$ 1,661	$ 7,906	$ 4,469
Operating expenses:
Research and development	6,537	4,917	12,813	8,626
General and administrative	2,973	1,702	6,375	3,690
Total operating expenses	9,510	6,619	19,188	12,316
Loss from operations	(7,988)	(4,958)	(11,282)	(7,847)
Other income (expense):
Interest and other income	90	52	154	49
Other expense, net	(2,184)	(73)	(5,377)	(111)
Total other expense, net	(2,094)	(21)	(5,223)	(62)
Net loss before income tax provision	(10,082)	(4,979)	(16,505)	(7,909)
Provision for (benefit from) income taxes	135		215	(396)
Net loss	(10,217)	(4,979)	(16,720)	(7,513)
Net loss attributable to ordinary shareholders	$ (10,217)	$ (4,979)	$ (16,720)	$ (7,513)
Net loss per share attributable to ordinary shareholders, basic and diluted	$ (1.40)	$ (11.85)	$ (4.08)	$ (18.38)
Weighted average ordinary shares outstanding, basic and diluted	7,298,139	420,063	4,101,564	408,807
Comprehensives Loss:
Net loss	$ (10,217)	$ (4,979)	$ (16,720)	$ (7,513)
Other comprehensive income (loss):
Foreign currency translation adjustment	(1,512)	(2,657)	(432)	(861)
Total comprehensive loss	$ (11,729)	$ (7,636)	$ (17,152)	$ (8,374)