Commitments and contingencies - Allowance for Credit Losses on Unfunded Commitments (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Commitments and Contingencies [Roll Forward]
Balance at beginning of period	$ 170,389	$ 31,139
Balance at end of period	157,954	89,141
Unfunded Commitments
Commitments and Contingencies [Roll Forward]
Balance at beginning of period	16,378	0
Impact of CECL adoption on provision for credit losses on unfunded commitments	0	2,947
Increase in provision for credit losses from unfunded commitments acquired in business combination	0	70
Provision for credit losses on unfunded commitments	(2,222)	1,601
Balance at end of period	$ 14,156	$ 4,618