Variable interest entities and securitization activities - Consolidated VIE Assets and Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Assets
Cash and cash equivalents	$ 308,428		$ 122,265
Restricted cash	62,961		$ 93,164
Loans, held for sale, at fair value	473,078	$ 340,288
Accrued interest	16,120	12,656
Other assets	20,134	9,346
Total Assets	8,016,955	5,372,095
Liabilities
Secured borrowings	2,064,785	1,294,243
Total Liabilities	6,818,709	4,537,887
Consolidated VIEs
Assets
Loans, net	2,877,837	2,472,807
Total Assets	2,898,727	2,518,743
Liabilities
Secured borrowings	2,211,923	1,905,749
Reportable Legal Entities | Consolidated VIEs
Assets
Cash and cash equivalents	14	20
Restricted cash	631	13,790
Loans, net	2,877,837	2,472,807
Real estate, held for sale	2,778	4,456
Other assets	17,467	27,670
Total Assets	2,898,727	2,518,743
Liabilities
Secured borrowings	2,211,923	1,905,749
Total Liabilities	$ 2,211,923	$ 1,905,749