Commitments and contingencies - Narrative (Details) - USD ($) $ in Millions |
12 Months Ended | ||||
---|---|---|---|---|---|
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
Jan. 10, 2018 |
Jun. 30, 2016 |
|
Commitments and Contingencies Disclosure [Abstract] | |||||
Operating leases, rent expense | $ 2.2 | $ 2.2 | $ 1.8 | ||
Funding agreement | Wellcome trust limited | |||||
Other contingencies | |||||
Development and regulatory milestone payments which the entity may be obligated to pay | $ 22.4 | $ 0.8 | |||
Subsequent Event | |||||
Other contingencies | |||||
Litigation settlement | $ 0.5 |