Variable interest entities and securitization activities - Consolidated VIE Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Assets
Cash and cash equivalents	$ 138,975	$ 67,928	$ 54,406
Restricted cash	47,697	51,728	$ 28,921
Loans, held for sale, at fair value	340,288	188,077
Accrued interest	12,656	10,583
Total Assets	5,372,095	4,977,018
Liabilities
Secured borrowings	1,370,519	1,189,392
Total Liabilities	4,537,887	4,132,234
Consolidated VIEs
Assets
Loans, net	2,472,807	2,326,199
Total Assets	2,518,743	2,378,486
Liabilities
Secured borrowings	1,905,749	1,815,154
Reportable Legal Entities | Consolidated VIEs
Assets
Cash and cash equivalents	20	23
Restricted cash	13,790	8,301
Loans, net	2,472,807	2,326,199
Loans, held for sale, at fair value		4,434
Real estate, held for sale	4,456
Due from servicers	10,995	27,964
Accrued interest	16,675	11,565
Total Assets	2,518,743	2,378,486
Liabilities
Secured borrowings	1,905,749	1,815,154
Total Liabilities	$ 1,905,749	$ 1,815,154