Commitments and contingencies (Narratives) (Details) - USD ($)	1 Months Ended	12 Months Ended
	Jan. 31, 2018	Dec. 31, 2019
Commitment And Contingencies [Line Items]
Losses for contingent liability		$ 0
Provision for a loss contingency		0
Dohmen Life Science Services
Commitment And Contingencies [Line Items]
Amount received under settlement agreement	$ 12,900,000
Dohmen Life Science Services | Other Receivable
Commitment And Contingencies [Line Items]
Net receivables outstanding		$ 12,900,000