Concentration of Credit Risk - Summary of Loans Held for Investment Portfolio by Loan Category Type (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Loans And Leases Receivable Disclosure [Line Items]
Loan commitment	$ 5,593,350	$ 5,411,944
Unfunded commitment	$ 463,042	$ 487,773
% of loan commitment	100.00%	100.00%
Loan UPB	$ 5,125,167	$ 4,919,343
% of loan UPB	100.00%	100.00%
Moderate Transitional
Loans And Leases Receivable Disclosure [Line Items]
Loan commitment	$ 1,948,162	$ 1,950,739
Unfunded commitment	$ 277,464	$ 294,693
% of loan commitment	34.80%	36.10%
Loan UPB	$ 1,671,871	$ 1,657,218
% of loan UPB	32.60%	33.70%
Bridge
Loans And Leases Receivable Disclosure [Line Items]
Loan commitment	$ 1,852,390	$ 1,646,895
Unfunded commitment	$ 47,509	$ 47,459
% of loan commitment	33.20%	30.40%
Loan UPB	$ 1,798,567	$ 1,593,436
% of loan UPB	35.10%	32.40%
Light Transitional
Loans And Leases Receivable Disclosure [Line Items]
Loan commitment	$ 1,757,798	$ 1,779,310
Unfunded commitment	$ 138,069	$ 145,621
% of loan commitment	31.40%	32.90%
Loan UPB	$ 1,619,729	$ 1,633,689
% of loan UPB	31.60%	33.20%
Construction
Loans And Leases Receivable Disclosure [Line Items]
Loan commitment	$ 35,000	$ 35,000
% of loan commitment	0.60%	0.60%
Loan UPB	$ 35,000	$ 35,000
% of loan UPB	0.70%	0.70%