Loans Receivable, Net - Property Type and Geographic Distribution of Properties Securing Loans in Portfolio (Detail) $ in Thousands	9 Months Ended
	Sep. 30, 2023 USD ($)	Sep. 30, 2023 security_loan	Sep. 30, 2023	Sep. 30, 2023 loan	Jun. 30, 2023 USD ($)	Mar. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2022 security_loan	Dec. 31, 2022	Dec. 31, 2022 loan	Sep. 30, 2022 USD ($)	Jun. 30, 2022 USD ($)	Mar. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans		185		185				203		203
Net Book Value	$ 23,715,901						$ 25,017,880
CECL reserve	(463,423)				$ (363,875)	$ (336,591)	(326,137)				$ (144,431)	$ (133,024)	$ (122,221)	$ (124,679)
Loans receivable, net	23,252,478						24,691,743
Total Loan Exposure	24,912,876						26,810,281
Net Loan Exposure	22,134,209						23,659,183
Percentage of portfolio			100.00%						100.00%
Principal balance	23,849,497						25,160,343
Total loan exposure including non-consolidated senior interests	1,100,000						1,600,000
Loan participations sold	275,697						224,744
Net loan exposure, asset-specific debt	935,400						950,300
Cost-recovery proceeds	40,733
Junior Loan Participation
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan participations sold	48,796
Senior Participations
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan participations sold	226,901						224,744
Subtotal
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | loan				145						160
Net Book Value	15,600,468						16,699,006
Total Loan Exposure	16,801,353						18,431,661
Net Loan Exposure	14,321,704						15,605,716
Percentage of portfolio			64.00%						66.00%
Sunbelt
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | loan				67						75
Net Book Value	5,811,609						6,538,034
Total Loan Exposure	5,971,930						6,802,928
Net Loan Exposure	5,644,980						6,244,886
Percentage of portfolio			25.00%						27.00%
Northeast
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | loan				32						36
Net Book Value	5,404,008						5,339,874
Total Loan Exposure	5,446,368						5,666,968
Net Loan Exposure	4,421,379						4,570,180
Percentage of portfolio			20.00%						19.00%
West
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | loan				31						33
Net Book Value	3,080,257						3,515,517
Total Loan Exposure	4,074,953						4,547,946
Net Loan Exposure	2,977,926						3,486,343
Percentage of portfolio			13.00%						15.00%
Midwest
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | loan				9						10
Net Book Value	944,028						987,718
Total Loan Exposure	943,954						1,091,882
Net Loan Exposure	915,330						984,151
Percentage of portfolio			4.00%						4.00%
Northwest
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | loan				6						6
Net Book Value	360,566						317,863
Total Loan Exposure	364,148						321,937
Net Loan Exposure	362,089						320,156
Percentage of portfolio			2.00%						1.00%
Subtotal
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | loan				40						43
Net Book Value	8,115,433						8,318,874
Total Loan Exposure	8,111,523						8,378,620
Net Loan Exposure	7,812,505						8,053,467
Percentage of portfolio			36.00%						34.00%
United Kingdom
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | loan				23						23
Net Book Value	3,511,992						3,362,629
Total Loan Exposure	3,486,567						3,393,126
Net Loan Exposure	3,240,731						3,123,925
Percentage of portfolio			15.00%						13.00%
Australia
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | loan				5						5
Net Book Value	1,343,580						1,405,601
Total Loan Exposure	1,352,700						1,417,318
Net Loan Exposure	1,346,196						1,408,565
Percentage of portfolio			6.00%						6.00%
Ireland
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | loan				3						3
Net Book Value	1,132,912						1,192,220
Total Loan Exposure	1,137,526						1,199,406
Net Loan Exposure	1,130,878						1,197,892
Percentage of portfolio			5.00%						5.00%
Spain
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | loan				3						4
Net Book Value	1,079,272						1,237,446
Total Loan Exposure	1,082,148						1,241,808
Net Loan Exposure	1,044,808						1,204,218
Percentage of portfolio			5.00%						5.00%
Sweden
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | loan				1						1
Net Book Value	451,731						473,374
Total Loan Exposure	454,222						476,673
Net Loan Exposure	453,891						476,367
Percentage of portfolio			2.00%						2.00%
Canada
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | loan										1
Net Book Value							49,409
Total Loan Exposure							49,432
Net Loan Exposure							49,398
Percentage of portfolio									0.00%
Other Europe
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | loan				5						6
Net Book Value	595,946						598,195
Total Loan Exposure	598,360						600,857
Net Loan Exposure	596,001						593,102
Percentage of portfolio			3.00%						3.00%
Office
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | loan				57						60
Net Book Value	9,206,553						9,082,946
Total Loan Exposure	10,016,113						10,023,495
Net Loan Exposure	8,006,364						8,099,334
Percentage of portfolio			36.00%						34.00%
Multifamily
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | loan				74						80
Net Book Value	5,908,559						6,214,123
Total Loan Exposure	6,068,116						6,330,153
Net Loan Exposure	5,855,896						6,189,298
Percentage of portfolio			26.00%						26.00%
Hospitality
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | loan				25						30
Net Book Value	4,184,422						4,879,314
Total Loan Exposure	4,219,762						4,908,583
Net Loan Exposure	3,891,569						4,552,404
Percentage of portfolio			17.00%						19.00%
Industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | loan				12						12
Net Book Value	2,121,085						2,140,636
Total Loan Exposure	2,133,209						2,236,716
Net Loan Exposure	2,124,686						2,150,501
Percentage of portfolio			10.00%						9.00%
Retail
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | loan				7						9
Net Book Value	842,100						1,098,315
Total Loan Exposure	859,681						1,141,932
Net Loan Exposure	830,697						1,090,238
Percentage of portfolio			4.00%						5.00%
Life Sciences / Studio
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | loan				4						4
Net Book Value	373,818						358,676
Total Loan Exposure	535,148						570,089
Net Loan Exposure	373,853						359,830
Percentage of portfolio			2.00%						2.00%
Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | loan				6						8
Net Book Value	1,079,364						1,243,870
Total Loan Exposure	1,080,847						1,599,313
Net Loan Exposure	$ 1,051,144						$ 1,217,578
Percentage of portfolio			5.00%						5.00%