Other Assets and Liabilities - Summary of Components of Other Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Accrued dividends payable	$ 97,350			$ 91,004
Accrued interest payable	25,772			20,548
Accrued management and incentive fees payable	19,342			19,158
Accounts payable and other liabilities	11,080			2,671
Current expected credit loss reserve for unfunded loan commitments	130,388	$ 128,945	$ 172,100	173,549	$ 177,026	$ 178,050	$ 112,694	$ 0
Derivative liabilities	355			58,915
Secured debt repayments pending servicer remittance	322			0
Total	159,424			202,327
Unfunded Loan Commitments [Member]
Current expected credit loss reserve for unfunded loan commitments	$ 5,203	$ 4,037	$ 11,021	$ 10,031	$ 12,057	$ 15,002	$ 22,536	$ 0