Commitments and contingencies - Other Agreements - (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2016 USD ($) multiple	Dec. 31, 2017 USD ($)	Sep. 30, 2016 USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Patent costs incurred	$ 0.5
Loss Contingency [Abstract]
Contingency reserves for litigation liabilities	0.0	$ 0.0
General and administrative
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Patent costs incurred	0.5	$ 0.6	$ 0.8
Various contract research organizations and institutions
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Milestone payable upon achievement	$ 0.1
Various contract research organizations and institutions | Minimum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of days written notice required by reporting entity to terminate agreement	30 days
Various contract research organizations and institutions | Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of days written notice required by reporting entity to terminate agreement	90 days
Non-profit organization agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Maximum funding				$ 4.0
Funding multiple | multiple				2.6
Milestone payment liability					$ 1.0
MRIC
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Amount of investment						$ 2.0