Revenue (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended				6 Months Ended
	Dec. 31, 2020	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020	Mar. 31, 2019	Jun. 30, 2021	Jun. 30, 2020
Revenue
Revenue accounted for under Topic 606		$ 8,243		$ 487		$ 10,772	$ 1,276
Product revenue, gross						17
Merck & Co | License Agreement
Revenue
Revenue accounted for under Topic 606						1,200
Collaboration revenue
Revenue
Revenue accounted for under Topic 606		813		7		2,815	152
Collaboration revenue | Sumitomo Pharmaceuticals (Suzhou) | License Agreement
Revenue
Revenue accounted for under Topic 606						1,600
Collaboration revenue - Upfront payment
Revenue
Revenue accounted for under Topic 606		6,940		(48)		7,070	108
Product revenue, gross		10,407		149		10,597	398
Collaboration revenue - Upfront payment | Sumitomo Pharmaceuticals (Suzhou) | License Agreement
Revenue
Revenue accounted for under Topic 606	$ 3,000		$ 1,000		$ 5,000
Research premium
Revenue
Revenue accounted for under Topic 606		$ 490		301		792	591
Government grants
Revenue
Revenue accounted for under Topic 606				$ 227		$ 95	$ 425