Loans Held-for-Investment by Property Type (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value	$ 3,978,862	$ 4,226,212
Percentage of Loan Portfolio	100.00%	100.00%
Office Building
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value	$ 1,758,637	$ 1,779,173
Percentage of Loan Portfolio	44.20%	42.00%
Multifamily
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value	$ 954,910	$ 1,058,708
Percentage of Loan Portfolio	24.00%	25.10%
Hotel
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value	$ 645,544	$ 640,503
Percentage of Loan Portfolio	16.20%	15.20%
Retail Site
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value	$ 336,064	$ 398,742
Percentage of Loan Portfolio	8.40%	9.40%
Industrial Property
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value	$ 244,706	$ 312,637
Percentage of Loan Portfolio	6.20%	7.40%
Other Property
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value	$ 39,001	$ 36,449
Percentage of Loan Portfolio	1.00%	0.90%