Concentration of Credit Risk - Summary of Loan Portfolio by Property Type (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Loans And Leases Receivable Disclosure [Line Items]
Loan Commitment	$ 5,318,297	$ 4,943,511
Unfunded Commitment	$ 488,916	$ 423,487
% of Loan Commitment	100.00%	100.00%
Loan UPB	$ 4,833,535	$ 4,524,725
% of Loan UPB	100.00%	100.00%
Office
Loans And Leases Receivable Disclosure [Line Items]
Loan Commitment	$ 2,811,920	$ 2,756,338
Unfunded Commitment	$ 401,705	$ 356,034
% of Loan Commitment	52.90%	55.70%
Loan UPB	$ 2,410,216	$ 2,400,304
% of Loan UPB	49.90%	53.00%
Multifamily
Loans And Leases Receivable Disclosure [Line Items]
Loan Commitment	$ 1,188,632	$ 804,838
Unfunded Commitment	$ 51,201	$ 24,001
% of Loan Commitment	22.30%	16.30%
Loan UPB	$ 1,137,731	$ 781,137
% of Loan UPB	23.50%	17.30%
Hotel
Loans And Leases Receivable Disclosure [Line Items]
Loan Commitment	$ 673,043	$ 737,293
Unfunded Commitment	$ 6,781	$ 9,864
% of Loan Commitment	12.70%	14.90%
Loan UPB	$ 669,773	$ 731,487
% of Loan UPB	13.90%	16.20%
Mixed Use
Loans And Leases Receivable Disclosure [Line Items]
Loan Commitment	$ 588,693	$ 586,993
Unfunded Commitment	$ 27,086	$ 31,398
% of Loan Commitment	11.10%	11.90%
Loan UPB	$ 561,606	$ 555,595
% of Loan UPB	11.60%	12.30%
Condominium
Loans And Leases Receivable Disclosure [Line Items]
Loan Commitment	$ 23,009	$ 25,049
% of Loan Commitment	0.40%	0.50%
Loan UPB	$ 23,009	$ 25,049
% of Loan UPB	0.50%	0.60%
Retail
Loans And Leases Receivable Disclosure [Line Items]
Loan Commitment	$ 33,000	$ 33,000
Unfunded Commitment	$ 2,143	$ 2,190
% of Loan Commitment	0.60%	0.70%
Loan UPB	$ 31,200	$ 31,153
% of Loan UPB	0.60%	0.70%