Commitments and contingencies - Other Agreements - (Details)	Sep. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)
Commitments and Contingencies
Maximum funding				$ 4,000,000
Funding multiple				2.6
Milestone payment liability	$ 0	$ 1,000,000
Loss Contingency [Abstract]
Contingency reserves for litigation liabilities	$ 0		$ 0