Loans Receivable, Net - Property Type and Geographic Distribution of Properties Securing Loans in Portfolio (Detail) $ in Thousands	9 Months Ended			12 Months Ended
	Sep. 30, 2024 USD ($) loan	Sep. 30, 2024 USD ($) security_loan	Sep. 30, 2024 USD ($)	Dec. 31, 2023 USD ($) loan	Dec. 31, 2023 USD ($) security_loan	Dec. 31, 2023 USD ($)	Jun. 30, 2024 USD ($)	Mar. 31, 2024 USD ($)	Sep. 30, 2023 USD ($)	Jun. 30, 2023 USD ($)	Mar. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans	149	149		178	178
Net book value	$ 21,602,517	$ 21,602,517	$ 21,602,517	$ 23,787,012	$ 23,787,012	$ 23,787,012
CECL reserve	(1,011,059)	(1,011,059)	(1,011,059)	(576,936)	(576,936)	(576,936)	$ (893,938)	$ (751,370)	$ (463,423)	$ (363,875)	$ (336,591)	$ (326,137)
Loans receivable, net	20,591,458	20,591,458	20,591,458	23,210,076	23,210,076	23,210,076
Total Loan Exposure	22,428,415	22,428,415	22,428,415	24,971,028	24,971,028	24,971,028
Net Loan Exposure	19,346,909	19,346,909	19,346,909	21,951,988	21,951,988	21,951,988
Principal balance	21,761,684	21,761,684	21,761,684	23,923,719	23,923,719	23,923,719
Total loan exposure including non-consolidated senior interests	770,200	770,200	770,200	1,100,000	1,100,000	1,100,000
Loan participations sold	103,500	103,500	103,500	337,721	337,721	337,721
Cost-recovery proceeds	99,000	99,000	99,000	53,000	53,000	53,000
Asset-specific debt, net
Accounts, Notes, Loans and Financing Receivable [Line Items]
Long-term debt	1,197,056	1,197,056	1,197,056	1,000,210	1,000,210	1,000,210
Junior Loan Participation
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan participations sold	$ 103,500	103,500	$ 103,500	100,924	100,924	100,924
Senior Participations
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan participations sold				$ 236,797	236,797	$ 236,797
Loan Exposure Risk | Financing Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net Loan Exposure Percentage of Portfolio			100.00%			100.00%
Subtotal
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | loan	117			141
Net book value	$ 14,435,383	14,435,383	$ 14,435,383	$ 15,460,479	15,460,479	$ 15,460,479
Total Loan Exposure	15,283,538	15,283,538	15,283,538	16,652,620	16,652,620	16,652,620
Net Loan Exposure	$ 12,276,927	12,276,927	$ 12,276,927	$ 13,951,306	13,951,306	$ 13,951,306
Subtotal | Loan Exposure Risk | Financing Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net Loan Exposure Percentage of Portfolio			64.00%			64.00%
Sunbelt
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | loan	55			65
Net book value	$ 5,236,391	5,236,391	$ 5,236,391	$ 5,658,172	5,658,172	$ 5,658,172
Total Loan Exposure	5,359,950	5,359,950	5,359,950	5,786,395	5,786,395	5,786,395
Net Loan Exposure	$ 4,815,460	4,815,460	$ 4,815,460	$ 5,402,732	5,402,732	$ 5,402,732
Sunbelt | Loan Exposure Risk | Financing Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net Loan Exposure Percentage of Portfolio			25.00%			25.00%
Northeast
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | loan	23			30
Net book value	$ 5,117,181	5,117,181	$ 5,117,181	$ 5,386,940	5,386,940	$ 5,386,940
Total Loan Exposure	5,174,073	5,174,073	5,174,073	5,426,951	5,426,951	5,426,951
Net Loan Exposure	$ 3,848,675	3,848,675	$ 3,848,675	$ 4,340,660	4,340,660	$ 4,340,660
Northeast | Loan Exposure Risk | Financing Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net Loan Exposure Percentage of Portfolio			20.00%			20.00%
West
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | loan	26			31
Net book value	$ 2,723,436	2,723,436	$ 2,723,436	$ 3,088,644	3,088,644	$ 3,088,644
Total Loan Exposure	3,381,514	3,381,514	3,381,514	4,108,074	4,108,074	4,108,074
Net Loan Exposure	$ 2,425,958	2,425,958	$ 2,425,958	$ 2,910,559	2,910,559	$ 2,910,559
West | Loan Exposure Risk | Financing Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net Loan Exposure Percentage of Portfolio			13.00%			13.00%
Midwest
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | loan	9			9
Net book value	$ 945,419	945,419	$ 945,419	$ 944,132	944,132	$ 944,132
Total Loan Exposure	951,628	951,628	951,628	945,222	945,222	945,222
Net Loan Exposure	$ 772,852	772,852	$ 772,852	$ 913,973	913,973	$ 913,973
Midwest | Loan Exposure Risk | Financing Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net Loan Exposure Percentage of Portfolio			4.00%			4.00%
Northwest
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | loan	4			6
Net book value	$ 412,956	412,956	$ 412,956	$ 382,591	382,591	$ 382,591
Total Loan Exposure	416,373	416,373	416,373	385,978	385,978	385,978
Net Loan Exposure	$ 413,982	413,982	$ 413,982	$ 383,382	383,382	$ 383,382
Northwest | Loan Exposure Risk | Financing Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net Loan Exposure Percentage of Portfolio			2.00%			2.00%
Subtotal
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | loan	32			37
Net book value	$ 7,167,134	7,167,134	$ 7,167,134	$ 8,326,533	8,326,533	$ 8,326,533
Total Loan Exposure	7,144,877	7,144,877	7,144,877	8,318,408	8,318,408	8,318,408
Net Loan Exposure	$ 7,069,982	7,069,982	$ 7,069,982	$ 8,000,682	8,000,682	$ 8,000,682
Subtotal | Loan Exposure Risk | Financing Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net Loan Exposure Percentage of Portfolio			36.00%			36.00%
United Kingdom
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | loan	17			20
Net book value	$ 3,130,712	3,130,712	$ 3,130,712	$ 3,470,120	3,470,120	$ 3,470,120
Total Loan Exposure	3,091,981	3,091,981	3,091,981	3,439,678	3,439,678	3,439,678
Net Loan Exposure	$ 3,072,996	3,072,996	$ 3,072,996	$ 3,181,489	3,181,489	$ 3,181,489
United Kingdom | Loan Exposure Risk | Financing Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net Loan Exposure Percentage of Portfolio			16.00%			14.00%
Australia
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | loan	3			5
Net book value	$ 1,026,894	1,026,894	$ 1,026,894	$ 1,429,144	1,429,144	$ 1,429,144
Total Loan Exposure	1,032,914	1,032,914	1,032,914	1,437,870	1,437,870	1,437,870
Net Loan Exposure	$ 1,029,221	1,029,221	$ 1,029,221	$ 1,432,146	1,432,146	$ 1,432,146
Australia | Loan Exposure Risk | Financing Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net Loan Exposure Percentage of Portfolio			5.00%			7.00%
Ireland
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | loan	3			3
Net book value	$ 1,112,988	1,112,988	$ 1,112,988	$ 1,191,068	1,191,068	$ 1,191,068
Total Loan Exposure	1,118,583	1,118,583	1,118,583	1,197,337	1,197,337	1,197,337
Net Loan Exposure	$ 1,111,325	1,111,325	$ 1,111,325	$ 1,188,554	1,188,554	$ 1,188,554
Ireland | Loan Exposure Risk | Financing Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net Loan Exposure Percentage of Portfolio			7.00%			5.00%
Spain
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | loan	3			3
Net book value	$ 852,586	852,586	$ 852,586	$ 1,117,790	1,117,790	$ 1,117,790
Total Loan Exposure	854,172	854,172	854,172	1,120,375	1,120,375	1,120,375
Net Loan Exposure	$ 813,041	813,041	$ 813,041	$ 1,078,811	1,078,811	$ 1,078,811
Spain | Loan Exposure Risk | Financing Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net Loan Exposure Percentage of Portfolio			4.00%			5.00%
Sweden
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | loan	1			1
Net book value	$ 467,303	467,303	$ 467,303	$ 474,262	474,262	$ 474,262
Total Loan Exposure	469,004	469,004	469,004	476,718	476,718	476,718
Net Loan Exposure	$ 468,624	468,624	$ 468,624	$ 476,281	476,281	$ 476,281
Sweden | Loan Exposure Risk | Financing Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net Loan Exposure Percentage of Portfolio			2.00%			2.00%
Other Europe
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | loan	4			5
Net book value	$ 519,158	519,158	$ 519,158	$ 644,149	644,149	$ 644,149
Total Loan Exposure	520,223	520,223	520,223	646,430	646,430	646,430
Net Loan Exposure	$ 517,134	517,134	$ 517,134	$ 643,401	643,401	$ 643,401
Other Europe | Loan Exposure Risk | Financing Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net Loan Exposure Percentage of Portfolio			2.00%			3.00%
Other International
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | loan	1
Net book value	$ 57,493	57,493	$ 57,493
Total Loan Exposure	58,000	58,000	58,000
Net Loan Exposure	$ 57,641	57,641	$ 57,641
Other International | Loan Exposure Risk | Financing Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net Loan Exposure Percentage of Portfolio			0.00%
Office
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | loan	47			54
Net book value	$ 8,684,237	8,684,237	$ 8,684,237	$ 9,253,609	9,253,609	$ 9,253,609
Total Loan Exposure	9,033,796	9,033,796	9,033,796	10,072,963	10,072,963	10,072,963
Net Loan Exposure	$ 6,807,782	6,807,782	$ 6,807,782	$ 7,956,472	7,956,472	$ 7,956,472
Office | Loan Exposure Risk | Financing Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net Loan Exposure Percentage of Portfolio			35.00%			36.00%
Multifamily
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | loan	62			73
Net book value	$ 5,620,111	5,620,111	$ 5,620,111	$ 5,876,128	5,876,128	$ 5,876,128
Total Loan Exposure	5,811,899	5,811,899	5,811,899	5,997,886	5,997,886	5,997,886
Net Loan Exposure	$ 5,471,558	5,471,558	$ 5,471,558	$ 5,756,192	5,756,192	$ 5,756,192
Multifamily | Loan Exposure Risk | Financing Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net Loan Exposure Percentage of Portfolio			28.00%			26.00%
Hospitality
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | loan	17			23
Net book value	$ 3,175,423	3,175,423	$ 3,175,423	$ 4,161,525	4,161,525	$ 4,161,525
Total Loan Exposure	3,217,014	3,217,014	3,217,014	4,194,588	4,194,588	4,194,588
Net Loan Exposure	$ 3,038,093	3,038,093	$ 3,038,093	$ 3,804,091	3,804,091	$ 3,804,091
Hospitality | Loan Exposure Risk | Financing Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net Loan Exposure Percentage of Portfolio			16.00%			17.00%
Industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | loan	10			12
Net book value	$ 2,086,785	2,086,785	$ 2,086,785	$ 2,189,808	2,189,808	$ 2,189,808
Total Loan Exposure	2,096,229	2,096,229	2,096,229	2,201,497	2,201,497	2,201,497
Net Loan Exposure	$ 2,062,923	2,062,923	$ 2,062,923	$ 2,190,914	2,190,914	$ 2,190,914
Industrial | Loan Exposure Risk | Financing Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net Loan Exposure Percentage of Portfolio			11.00%			10.00%
Retail
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | loan	5			6
Net book value	$ 693,991	693,991	$ 693,991	$ 814,241	814,241	$ 814,241
Total Loan Exposure	721,638	721,638	721,638	834,825	834,825	834,825
Net Loan Exposure	$ 660,935	660,935	$ 660,935	$ 785,573	785,573	$ 785,573
Retail | Loan Exposure Risk | Financing Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net Loan Exposure Percentage of Portfolio			3.00%			4.00%
Life Sciences / Studio
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | loan	4			4
Net book value	$ 401,890	401,890	$ 401,890	$ 385,098	385,098	$ 385,098
Total Loan Exposure	606,999	606,999	606,999	561,517	561,517	561,517
Net Loan Exposure	$ 400,303	400,303	$ 400,303	$ 384,219	384,219	$ 384,219
Life Sciences / Studio | Loan Exposure Risk | Financing Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net Loan Exposure Percentage of Portfolio			2.00%			2.00%
Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | loan	4			6
Net book value	$ 940,080	940,080	$ 940,080	$ 1,106,603	1,106,603	$ 1,106,603
Total Loan Exposure	940,840	940,840	940,840	1,107,752	1,107,752	1,107,752
Net Loan Exposure	$ 905,315	$ 905,315	$ 905,315	$ 1,074,527	$ 1,074,527	$ 1,074,527
Other | Loan Exposure Risk | Financing Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net Loan Exposure Percentage of Portfolio			5.00%			5.00%