Commitments and contingencies - Other Agreements - (Details) $ in Millions	1 Months Ended
	Sep. 30, 2016 USD ($) multiple	Mar. 31, 2018 USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Funding multiple | multiple	2.6
Various contract research organizations and institutions
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Funding possible upon achievement of milestones	$ 4.0
Deferred revenue		$ 1.0