Commitments and contingencies Commitments and contingencies - Credit Losses (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Commitments and Contingencies [Roll Forward]
Balance at beginning of period	$ 89,141	$ 31,139
Balance at end of period	113,129	113,129
Unfunded Commitments
Commitments and Contingencies [Roll Forward]
Balance at beginning of period	4,618	0
Initial recognition of allowance for credit losses			$ 0	$ 2,947
Increase from unfunded commitments acquired in business combination	0	70
Provision for credit losses on unfunded commitments	1,882	3,483
Balance at end of period	$ 6,500	$ 6,500