Loans Receivable, Net - Overall Statistics for Loans Receivable Portfolio (Detail) $ in Thousands	9 Months Ended				12 Months Ended
	Sep. 30, 2024 USD ($)	Sep. 30, 2024 USD ($) loan	Sep. 30, 2024 USD ($) security_loan	Sep. 30, 2024 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2023 USD ($) loan	Dec. 31, 2023 USD ($) security_loan	Dec. 31, 2023 USD ($)	Sep. 30, 2023 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans		149	149			178	178
Principal balance	$ 21,761,684	$ 21,761,684	$ 21,761,684	$ 21,761,684	$ 23,923,719	$ 23,923,719	$ 23,923,719	$ 23,923,719
Financing Receivable, Excluding Accrued Interest, after Allowance for Credit Loss	20,591,458	20,591,458	20,591,458	20,591,458	23,210,076	23,210,076	23,210,076	23,210,076
Current expected credit loss reserves for unfunded loan commitments	$ 8,307	$ 8,307	$ 8,307	$ 8,307	$ 15,371	$ 15,371	$ 15,371	$ 15,371	$ 13,600
Weighted-average cash coupon (percentage)	3.40%	3.40%	3.40%	3.40%	3.37%	3.37%	3.37%	3.37%
Weighted-average all-in yield (percentage)				3.74%				3.71%
Weighted-average maximum maturity (years)	2 years 2 months 12 days				2 years 6 months
Debt instrument, variable interest rate, type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR)				Secured Overnight Financing Rate (SOFR)
Percent of loans subject to prepayment restrictions	14.00%	14.00%	14.00%	14.00%	14.00%	14.00%	14.00%	14.00%
Percent of loans not subject to prepayment restrictions	86.00%	86.00%	86.00%	86.00%	86.00%	86.00%	86.00%	86.00%
Interest Rate Swaps
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notional amount	$ 229,900	$ 229,900	$ 229,900	$ 229,900	$ 229,900	$ 229,900	$ 229,900	$ 229,900
Unfunded Loan Commitment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | loan		76
Current expected credit loss reserves for unfunded loan commitments	$ 1,562,589	$ 1,562,589	$ 1,562,589	$ 1,562,589	$ 2,430,664	$ 2,430,664	$ 2,430,664	$ 2,430,664