Loans Receivable, Net - Property Type and Geographic Distribution of Properties Securing Loans in Portfolio (Detail) $ in Thousands	Sep. 30, 2022 USD ($) SecurityLoan	Jun. 30, 2022 USD ($)	Mar. 31, 2022 USD ($)	Dec. 31, 2021 USD ($) SecurityLoan	Sep. 30, 2021 USD ($)	Jun. 30, 2021 USD ($)	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	205			188
Principal balance	$ 24,423,133			$ 22,003,017
CECL reserve	(144,431)	$ (133,024)	$ (122,221)	(124,679)	$ (130,388)	$ (128,945)	$ (172,100)	$ (173,549)
Loans receivable, net	24,278,702			21,878,338
Total Loan Exposure	$ 26,136,006			$ 23,669,111
Percentage of Portfolio	100.00%			100.00%
Total loan exposure including senior interests	$ 1,600,000			$ 1,500,000
2018 Single Asset Securitization
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loan amount, securitized				$ 379,300
Subtotal
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	164			156
Principal balance	$ 16,644,147			$ 15,357,571
Total Loan Exposure	$ 18,298,257			$ 16,706,378
Percentage of Portfolio	70.00%			71.00%
Sunbelt
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	76			71
Principal balance	$ 6,439,282			$ 5,907,230
Total Loan Exposure	$ 6,688,040			$ 6,206,216
Percentage of Portfolio	26.00%			26.00%
Northeast
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	38			37
Principal balance	$ 5,365,371			$ 4,615,076
Total Loan Exposure	$ 5,694,075			$ 4,934,295
Percentage of Portfolio	22.00%			21.00%
West
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	34			33
Principal balance	$ 3,516,562			$ 3,520,942
Total Loan Exposure	$ 4,484,044			$ 4,199,208
Percentage of Portfolio	17.00%			18.00%
Midwest
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	10			10
Principal balance	$ 1,005,315			$ 1,063,202
Total Loan Exposure	$ 1,110,161			$ 1,113,959
Percentage of Portfolio	4.00%			5.00%
Northwest
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	6			5
Principal balance	$ 317,617			$ 251,121
Total Loan Exposure	$ 321,937			$ 252,700
Percentage of Portfolio	1.00%			1.00%
Subtotal
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	41			32
Principal balance	$ 7,778,986			$ 6,645,446
Total Loan Exposure	$ 7,837,749			$ 6,962,733
Percentage of Portfolio	30.00%			29.00%
United Kingdom
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	22			17
Principal balance	$ 3,122,227			$ 2,342,146
Total Loan Exposure	$ 3,153,449			$ 2,598,033
Percentage of Portfolio	12.00%			11.00%
Australia
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	6			4
Principal balance	$ 1,362,111			$ 504,668
Total Loan Exposure	$ 1,373,933			$ 509,885
Percentage of Portfolio	5.00%			2.00%
Spain
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	4			4
Principal balance	$ 1,147,064			$ 1,374,364
Total Loan Exposure	$ 1,151,521			$ 1,380,763
Percentage of Portfolio	5.00%			6.00%
Ireland
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	3			1
Principal balance	$ 1,117,526			$ 1,210,375
Total Loan Exposure	$ 1,122,990			$ 1,216,864
Percentage of Portfolio	4.00%			5.00%
Sweden
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	1			1
Principal balance	$ 444,948			$ 546,319
Total Loan Exposure	$ 448,264			$ 551,149
Percentage of Portfolio	2.00%			2.00%
Canada
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	1			2
Principal balance	$ 48,396			$ 68,558
Total Loan Exposure	$ 48,449			$ 68,478
Percentage of Portfolio	0.00%			0.00%
Other Europe
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	4			3
Principal balance	$ 536,714			$ 599,016
Total Loan Exposure	$ 539,143			$ 637,561
Percentage of Portfolio	2.00%			3.00%
Office
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	67			65
Principal balance	$ 9,609,121			$ 9,473,039
Total Loan Exposure	$ 10,697,145			$ 10,425,026
Percentage of Portfolio	41.00%			44.00%
Multifamily
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	81			75
Principal balance	$ 6,210,730			$ 5,721,260
Total Loan Exposure	$ 6,313,319			$ 5,771,517
Percentage of Portfolio	24.00%			24.00%
Hospitality
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	30			25
Principal balance	$ 4,840,022			$ 3,427,245
Total Loan Exposure	$ 4,871,384			$ 3,540,391
Percentage of Portfolio	19.00%			15.00%
Industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	10			6
Principal balance	$ 1,659,162			$ 1,102,452
Total Loan Exposure	$ 1,752,418			$ 1,185,606
Percentage of Portfolio	7.00%			5.00%
Retail
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	9			8
Principal balance	$ 1,093,758			$ 871,241
Total Loan Exposure	$ 1,134,337			$ 909,970
Percentage of Portfolio	4.00%			4.00%
Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	8			9
Principal balance	$ 1,010,340			$ 1,407,780
Total Loan Exposure	$ 1,367,403			$ 1,836,601
Percentage of Portfolio	5.00%			8.00%