Schedule IV - Mortgage Loans on Real Estate (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior Liens	$ 1,512,675,000
Face Amount of Loans	22,156,437,000
Carrying Amount of Loans	22,003,017,000	$ 16,572,715,000	$ 16,164,801,000	$ 14,191,200,000
CECL reserve	(124,679,000)	(173,549,000)	0
Total Loans, Net	21,878,338,000	$ 16,399,166,000	$ 16,164,801,000
Senior loans less than 3% of the carrying amount of total loans
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior Liens	0
Face Amount of Loans	19,753,327,000
Carrying Amount of Loans	19,610,889,000
Senior Mortgage Loans
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior Liens	0
Face Amount of Loans	21,735,353,000
Carrying Amount of Loans	21,587,418,000
Subordinate Loans
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior Liens	1,512,675,000
Face Amount of Loans	421,084,000
Carrying Amount of Loans	$ 415,599,000
Office | Senior loans less than 3% of the carrying amount of total loans
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest Payment Rates, Fixed	4.46%
Prior Liens	$ 0
Face Amount of Loans	7,922,784,000
Carrying Amount of Loans	7,873,811,000
Mixed Use | Senior loans less than 3% of the carrying amount of total loans
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior Liens	0
Face Amount of Loans	1,045,590,000
Carrying Amount of Loans	$ 1,041,047,000
Multifamily | Senior loans less than 3% of the carrying amount of total loans
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest Payment Rates, Fixed	1.50%
Prior Liens	$ 0
Face Amount of Loans	5,162,805,000
Carrying Amount of Loans	5,115,567,000
Hospitality | Senior loans less than 3% of the carrying amount of total loans
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior Liens	0
Face Amount of Loans	3,311,723,000
Carrying Amount of Loans	3,288,135,000
Industrial | Senior loans less than 3% of the carrying amount of total loans
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior Liens	0
Face Amount of Loans	1,076,179,000
Carrying Amount of Loans	1,067,608,000
Retail | Senior loans less than 3% of the carrying amount of total loans
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior Liens	0
Face Amount of Loans	409,917,000
Carrying Amount of Loans	406,311,000
Other | Senior loans less than 3% of the carrying amount of total loans
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Prior Liens	0
Face Amount of Loans	824,329,000
Carrying Amount of Loans	$ 818,410,000
Various | Subordinate Loans
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest Payment Rates, Fixed	5.74%
Prior Liens	$ 1,512,675,000
Face Amount of Loans	421,084,000
Carrying Amount of Loans	$ 415,599,000
Ireland | Office | Borrower A | Senior loans in excess of 3% of the carrying amount of total loans
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest Payment Rates	2.54%
Prior Liens	$ 0
Face Amount of Loans	1,160,153,000
Carrying Amount of Loans	$ 1,155,748,000
Spain | Mixed Use | Borrower B | Senior loans in excess of 3% of the carrying amount of total loans
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest Payment Rates	3.25%
Prior Liens	$ 0
Face Amount of Loans	821,873,000
Carrying Amount of Loans	$ 820,781,000
Minimum | Office | Senior loans less than 3% of the carrying amount of total loans
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest Payment Rates	2.18%
Minimum | Mixed Use | Senior loans less than 3% of the carrying amount of total loans
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest Payment Rates	2.50%
Minimum | Multifamily | Senior loans less than 3% of the carrying amount of total loans
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest Payment Rates	1.60%
Minimum | Hospitality | Senior loans less than 3% of the carrying amount of total loans
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest Payment Rates	2.20%
Minimum | Industrial | Senior loans less than 3% of the carrying amount of total loans
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest Payment Rates	2.60%
Minimum | Retail | Senior loans less than 3% of the carrying amount of total loans
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest Payment Rates	2.25%
Minimum | Other | Senior loans less than 3% of the carrying amount of total loans
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest Payment Rates	3.00%
Minimum | Spain | Office | Borrower A | Senior loans in excess of 3% of the carrying amount of total loans
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest Payment Rates	2.65%
Maximum | Office | Senior loans less than 3% of the carrying amount of total loans
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest Payment Rates	6.13%
Maximum | Mixed Use | Senior loans less than 3% of the carrying amount of total loans
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest Payment Rates	5.00%
Maximum | Multifamily | Senior loans less than 3% of the carrying amount of total loans
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest Payment Rates	5.25%
Maximum | Hospitality | Senior loans less than 3% of the carrying amount of total loans
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest Payment Rates	4.30%
Maximum | Industrial | Senior loans less than 3% of the carrying amount of total loans
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest Payment Rates	3.25%
Maximum | Retail | Senior loans less than 3% of the carrying amount of total loans
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest Payment Rates	3.10%
Maximum | Other | Senior loans less than 3% of the carrying amount of total loans
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest Payment Rates	4.60%
Maximum | Spain | Office | Borrower A | Senior loans in excess of 3% of the carrying amount of total loans
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest Payment Rates	4.00%