Asset-Specific Debt Agreements, Net - Summary of Asset-Specific Financings (Detail) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2021 USD ($) SecurityLoan	Dec. 31, 2020 USD ($) SecurityLoan
Participating Mortgage Loans [Line Items]
Financing provided, Principal Balance	$ 8,142,728	$ 7,896,863
Asset Specific Financings [Member]
Participating Mortgage Loans [Line Items]
Count | SecurityLoan	4	4
Financing provided, Principal Balance	$ 438,433	$ 399,699
Financing provided	2023-12	2023-10
Financing provided, Book Value	$ 430,448	$ 391,269
LIBOR [Member] | Asset Specific Financings [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Yield/Cost Rate	3.43%	3.48%
Collateral Assets [Member]
Participating Mortgage Loans [Line Items]
Count | SecurityLoan	4	4
Collateral assets, Book Value	$ 552,989	$ 499,085
Financing provided	2023-12	2023-10
Collateral assets, Principal Balance	$ 566,170	$ 512,794
Collateral Assets [Member] | LIBOR [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Yield/Cost Rate	4.62%	4.65%