Loans Receivable, Net - Net Book Value, Total Loan Exposure and Net Loan Exposure of Loans Receivable Based on Internal Risk Ratings (Detail) $ in Thousands	9 Months Ended
	Sep. 30, 2023 USD ($)	Sep. 30, 2023 security_loan	Sep. 30, 2023 loan	Jun. 30, 2023 USD ($)	Mar. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2022 security_loan	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
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
1
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | loan			15					17
Net Book Value	763,494					1,403,185
Total Loan Exposure	812,060					1,428,232
Net Loan Exposure	764,174					1,170,725
2
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | loan			40					36
Net Book Value	6,102,290					5,880,424
Total Loan Exposure	6,578,639					6,562,852
Net Loan Exposure	5,105,664					5,292,933
3
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | loan			107					134
Net Book Value	12,493,474					14,128,133
Total Loan Exposure	13,120,942					15,209,018
Net Loan Exposure	12,281,191					13,826,730
4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | loan			13					11
Net Book Value	2,965,121					2,677,027
Total Loan Exposure	2,967,865					2,680,145
Net Loan Exposure	2,913,093					2,628,539
5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | loan			10					5
Net Book Value	1,391,522					929,111
Total Loan Exposure	1,433,370					930,034
Net Loan Exposure	$ 1,070,087					$ 740,256