Commitments and contingencies - Allowance for Credit Losses on Unfunded Commitments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Commitments and Contingencies [Roll Forward]
Balance at beginning of period	$ 157,954	$ 89,141	$ 170,389	$ 31,139
Balance at end of period	144,663	113,129	144,663	113,129
Unfunded Commitments
Commitments and Contingencies [Roll Forward]
Balance at beginning of period	14,156	4,618	16,378	0
Impact of CECL adoption on provision for credit losses on unfunded commitments	0	0	0	2,947
Increase in provision for credit losses from unfunded commitments acquired in business combination	0	0	0	70
Provision for credit losses on unfunded commitments	(954)	1,882	(3,176)	3,483
Balance at end of period	$ 13,202	$ 6,500	$ 13,202	$ 6,500