Concentration of Credit Risk - Summary of Loans Held for Investment Portfolio by Property Type (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	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%
Office
Loans And Leases Receivable Disclosure [Line Items]
Loan commitment	$ 1,928,630	$ 2,265,187
Unfunded commitment	$ 142,168	$ 178,878
% of loan commitment	37.20%	41.90%
Outstanding principal	$ 1,786,462	$ 2,086,309
% of loan UPB	37.80%	42.40%
Multifamily
Loans And Leases Receivable Disclosure [Line Items]
Loan commitment	$ 1,865,326	$ 1,595,643
Unfunded commitment	$ 133,194	$ 121,211
% of loan commitment	36.00%	29.50%
Outstanding principal	$ 1,732,132	$ 1,474,731
% of loan UPB	36.80%	30.00%
Hotel
Loans And Leases Receivable Disclosure [Line Items]
Loan commitment	$ 493,944	$ 658,943
Unfunded commitment	$ 4,000	$ 4,000
% of loan commitment	9.50%	12.20%
Outstanding principal	$ 492,359	$ 657,672
% of loan UPB	10.50%	13.40%
Life Science
Loans And Leases Receivable Disclosure [Line Items]
Loan commitment	$ 404,600	$ 494,600
Unfunded commitment	$ 146,367	$ 163,860
% of loan commitment	7.80%	9.10%
Outstanding principal	$ 258,233	$ 330,740
% of loan UPB	5.50%	6.70%
Mixed-Use
Loans And Leases Receivable Disclosure [Line Items]
Loan commitment	$ 285,340	$ 347,408
Unfunded commitment	$ 15,230	$ 17,681
% of loan commitment	5.50%	6.40%
Outstanding principal	$ 270,110	$ 329,728
% of loan UPB	5.70%	6.70%
Industrial
Loans And Leases Receivable Disclosure [Line Items]
Loan commitment	$ 113,000
Unfunded commitment	$ 6,167
% of loan commitment	2.20%
Outstanding principal	$ 106,833
% of loan UPB	2.30%
Other
Loans And Leases Receivable Disclosure [Line Items]
Loan commitment	$ 50,600
Unfunded commitment	$ 21,600
% of loan commitment	1.00%
Outstanding principal	$ 29,000
% of loan UPB	0.60%
Retail
Loans And Leases Receivable Disclosure [Line Items]
Loan commitment	$ 33,000	$ 33,000
Unfunded commitment	$ 2,143	$ 2,143
% of loan commitment	0.60%	0.60%
Outstanding principal	$ 23,000	$ 23,000
% of loan UPB	0.50%	0.50%
Non-drawable outstanding unfunded loan commitments	$ 2,100	$ 2,100
Condominium
Loans And Leases Receivable Disclosure [Line Items]
Loan commitment	12,032	17,163
Unfunded commitment	$ 0	$ 0
% of loan commitment	0.20%	0.30%
Outstanding principal	$ 12,032	$ 17,163
% of loan UPB	0.30%	0.30%
Participation interests in whole mortgage loans related to one project and borrower (in percent)	24.00%	24.00%