Loans and Allowance for Credit Losses - Allowance for loan losses by loan product and impairment methodology (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Allowance for loan losses
General	$ 27,403	$ 29,539
Specific	18,246	17,193
Ending Balance	45,649	46,732	$ 57,968	$ 7,441
Originated SBC loans
Allowance for loan losses
General	2,729	2,640
Specific	5,243	6,200
Ending Balance	7,972	8,840	10,362	304
Originated Transitional loans
Allowance for loan losses
General	14,848	14,995
Specific	2,195
Ending Balance	17,043	14,995	24,264	188
Acquired loans
Allowance for loan losses
General	4,335	5,457
Specific	2,700	2,840
Ending Balance	7,035	8,297	10,646	3,054
Acquired SBA 7(a) loans
Allowance for loan losses
General	627	767
Specific	3,695	3,782
Ending Balance	4,322	4,549	5,622	2,114
Originated SBA 7(a) loans
Allowance for loan losses
General	4,864	5,680
Specific	4,413	4,371
Ending Balance	$ 9,277	$ 10,051	$ 7,074	$ 1,781