Commitments and contingencies Commitments and contingencies - Credit Losses (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Jan. 01, 2020	Jan. 01, 2019
Commitments and Contingencies [Roll Forward]
Balance at beginning of period	$ 31,139
Impact of CECL adoption on provision for credit losses on unfunded commitments		$ (25,018)	$ (1,309)
Balance at end of period	89,141
Unfunded Commitments
Commitments and Contingencies [Roll Forward]
Balance at beginning of period	0
Impact of CECL adoption on provision for credit losses on unfunded commitments		$ 2,947
Increase from unfunded commitments acquired in business combination	70
Provision for credit losses on unfunded commitments	1,601
Balance at end of period	$ 4,618