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		12 Months Ended
	Sep. 30, 2024 USD ($) loan	Sep. 30, 2024 USD ($) security_loan	Dec. 31, 2023 USD ($) loan	Dec. 31, 2023 USD ($) security_loan	Jun. 30, 2024 USD ($)	Mar. 31, 2024 USD ($)	Sep. 30, 2023 USD ($)	Jun. 30, 2023 USD ($)	Mar. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Financing Receivable, Credit Quality Indicator [Line Items]
Number of loans	149	149	178	178
Net book value	$ 21,602,517	$ 21,602,517	$ 23,787,012	$ 23,787,012
CECL reserve	(1,011,059)	(1,011,059)	(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	23,210,076	23,210,076
Total loan exposure	22,428,415	22,428,415	24,971,028	24,971,028
Net loan exposure	19,346,909	19,346,909	21,951,988	21,951,988
Principal balance	21,761,684	21,761,684	23,923,719	23,923,719
Total loan exposure including non-consolidated senior interests	770,200	770,200	1,100,000	1,100,000
Loan participations sold	103,500	103,500	337,721	337,721
Cost-recovery proceeds	99,000	99,000	53,000	53,000
Junior Loan Participation
Financing Receivable, Credit Quality Indicator [Line Items]
Loan participations sold	103,500	103,500	100,924	100,924
Senior Participations
Financing Receivable, Credit Quality Indicator [Line Items]
Loan participations sold			236,797	236,797
Asset-specific debt, net
Financing Receivable, Credit Quality Indicator [Line Items]
Securitized debt obligations, net	$ 1,197,056	1,197,056	$ 1,000,210	1,000,210
1
Financing Receivable, Credit Quality Indicator [Line Items]
Number of loans | loan	16		15
Net book value	$ 2,058,795	2,058,795	$ 763,101	763,101
Total loan exposure	2,062,324	2,062,324	811,217	811,217
Net loan exposure	$ 1,139,470	1,139,470	$ 763,223	763,223
2
Financing Receivable, Credit Quality Indicator [Line Items]
Number of loans | loan	26		36
Net book value	$ 3,938,950	3,938,950	$ 6,143,184	6,143,184
Total loan exposure	3,947,816	3,947,816	6,618,319	6,618,319
Net loan exposure	$ 3,944,699	3,944,699	$ 5,095,395	5,095,395
3
Financing Receivable, Credit Quality Indicator [Line Items]
Number of loans | loan	67		99
Net book value	$ 9,595,696	9,595,696	$ 12,277,518	12,277,518
Total loan exposure	9,783,847	9,783,847	12,573,282	12,573,282
Net loan exposure	$ 9,192,975	9,192,975	$ 11,964,620	11,964,620
4
Financing Receivable, Credit Quality Indicator [Line Items]
Number of loans | loan	20		15
Net book value	$ 2,843,464	2,843,464	$ 2,725,930	2,725,930
Total loan exposure	3,365,798	3,365,798	3,036,837	3,036,837
Net loan exposure	$ 2,783,690	2,783,690	$ 2,668,025	2,668,025
5
Financing Receivable, Credit Quality Indicator [Line Items]
Number of loans | loan	20		13
Net book value	$ 3,165,612	3,165,612	$ 1,877,279	1,877,279
Total loan exposure	3,268,630	3,268,630	1,931,373	1,931,373
Net loan exposure	$ 2,286,075	$ 2,286,075	$ 1,460,725	$ 1,460,725