Concentration of Credit Risk - Summary of Loans Held for Investment Portfolio by Property Type (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Loans And Leases Receivable Disclosure [Line Items]
Loan commitment	$ 4,869,045	$ 5,429,146
Unfunded commitment	$ 300,502	$ 426,061
% of loan commitment	100.00%	100.00%
Total unpaid principal balance	$ 4,567,250	$ 5,004,798
% of loan UPB	100.00%	100.00%
Multifamily
Loans And Leases Receivable Disclosure [Line Items]
Loan commitment	$ 2,177,293	$ 2,491,441
Unfunded commitment	$ 83,984	$ 110,769
% of loan commitment	44.80%	46.00%
Total unpaid principal balance	$ 2,093,309	$ 2,380,672
% of loan UPB	45.70%	47.50%
Office
Loans And Leases Receivable Disclosure [Line Items]
Loan commitment	$ 1,217,159	$ 1,553,378
Unfunded commitment	$ 97,760	$ 155,986
% of loan commitment	25.00%	28.50%
Total unpaid principal balance	$ 1,116,934	$ 1,397,392
% of loan UPB	24.60%	28.00%
Hotel
Loans And Leases Receivable Disclosure [Line Items]
Loan commitment	$ 568,543	$ 483,743
Unfunded commitment	$ 11,740	$ 11,666
% of loan commitment	11.70%	8.90%
Total unpaid principal balance	$ 557,975	$ 473,790
% of loan UPB	12.20%	9.50%
Life Science
Loans And Leases Receivable Disclosure [Line Items]
Loan commitment	$ 404,600	$ 404,600
Unfunded commitment	$ 60,716	$ 93,092
% of loan commitment	8.30%	7.50%
Total unpaid principal balance	$ 343,884	$ 311,508
% of loan UPB	7.50%	6.20%
Mixed-Use
Loans And Leases Receivable Disclosure [Line Items]
Loan commitment	$ 274,850	$ 283,340
Unfunded commitment	$ 14,568	$ 15,061
% of loan commitment	5.60%	5.20%
Total unpaid principal balance	$ 260,282	$ 268,279
% of loan UPB	5.70%	5.40%
Industrial
Loans And Leases Receivable Disclosure [Line Items]
Loan commitment	$ 107,000	$ 93,044
Unfunded commitment	$ 9,436	$ 5,987
% of loan commitment	2.20%	1.70%
Total unpaid principal balance	$ 97,564	$ 87,057
% of loan UPB	2.10%	1.70%
Self Storage
Loans And Leases Receivable Disclosure [Line Items]
Loan commitment	$ 69,000	$ 69,000
Unfunded commitment	$ 2,000	$ 11,900
% of loan commitment	1.40%	1.30%
Total unpaid principal balance	$ 67,000	$ 57,100
% of loan UPB	1.50%	1.10%
Other
Loans And Leases Receivable Disclosure [Line Items]
Loan commitment	$ 50,600	$ 50,600
Unfunded commitment	$ 20,298	$ 21,600
% of loan commitment	1.00%	0.90%
Total unpaid principal balance	$ 30,302	$ 29,000
% of loan UPB	0.70%	0.60%