Collaboration and license arrangements (Details) $ in Thousands		1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 06, 2018 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2015 USD ($) item agreement
Collaboration and license arrangements
Revenue			$ 14,944	$ 10,591	$ 40,816	$ 26,755
Joint development and license agreement
Collaboration and license arrangements
Consideration on collaboration activities					3,200
Revenue	$ 1,600
Evaluation and option agreements and license agreement
Collaboration and license arrangements
Revenue		$ 1,800
Number of agreements | agreement								3
Number of fields for which the agreements were entered | item								3
Non-refundable license fee		1,000						$ 2,000
Amount allocated to the option of the related field		$ 800
Deferred revenue			$ 1,200		$ 1,200		$ 1,200
Exclusive agreement
Collaboration and license arrangements
Consideration on collaboration activities							$ 500