Concentration of Credit Risk - Summary of Geographic Composition of Loans Held for Investment Based on Current UPB and Loan Commitment (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Loans And Leases Receivable Disclosure [Line Items]
Loan commitment	$ 5,186,472	$ 5,411,944
Unfunded commitment	$ 470,869	$ 487,773
% of loan commitment	100.00%	100.00%
Outstanding principal	$ 4,710,161	$ 4,919,343
% of loan UPB	100.00%	100.00%
East
Loans And Leases Receivable Disclosure [Line Items]
Loan commitment	$ 1,942,462	$ 1,925,457
Unfunded commitment	$ 71,429	$ 63,459
% of loan commitment	37.50%	35.60%
Outstanding principal	$ 1,872,204	$ 1,863,172
% of loan UPB	39.70%	37.80%
West
Loans And Leases Receivable Disclosure [Line Items]
Loan commitment	$ 1,510,326	$ 1,484,883
Unfunded commitment	$ 249,692	$ 244,100
% of loan commitment	29.10%	27.40%
Outstanding principal	$ 1,253,479	$ 1,233,628
% of loan UPB	26.60%	25.10%
South
Loans And Leases Receivable Disclosure [Line Items]
Loan commitment	$ 1,290,922	$ 1,323,800
Unfunded commitment	$ 106,851	$ 115,714
% of loan commitment	24.90%	24.50%
Outstanding principal	$ 1,184,613	$ 1,208,940
% of loan UPB	25.20%	24.60%
Midwest
Loans And Leases Receivable Disclosure [Line Items]
Loan commitment	$ 372,762	$ 677,804
Unfunded commitment	$ 36,730	$ 64,500
% of loan commitment	7.20%	12.50%
Outstanding principal	$ 336,032	$ 613,603
% of loan UPB	7.10%	12.50%
Various
Loans And Leases Receivable Disclosure [Line Items]
Loan commitment	$ 70,000
Unfunded commitment	$ 6,167
% of loan commitment	1.30%
Outstanding principal	$ 63,833
% of loan UPB	1.40%