Collaboration agreements - Merck KGaA (Details) - Merck KGaA	1 Months Ended
	Jun. 30, 2014 USD ($) target	Mar. 31, 2022 USD ($) target	Dec. 31, 2018 target	Dec. 31, 2014 USD ($)
Collaboration agreements
Proceeds from Collaborators	$ 12,000,000
Amount of additional fees receivable when target is designated and commercial license to target is granted				$ 0
Number of targets designated | target	6	6	6
Next potential development milestone payment eligible to receive		$ 500,000