Securitized Debt Obligations, Net (Detail) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2024 USD ($) loan	Sep. 30, 2023 USD ($)	Dec. 31, 2023 USD ($) loan
Debt Instrument [Line Items]
Debt instrument, variable interest rate, type [Extensible Enumeration]			Secured Overnight Financing Rate (SOFR)		Secured Overnight Financing Rate (SOFR)
Securitized debt obligations, net
Debt Instrument [Line Items]
Count | loan			3		3
Count | loan			53		56
Principal Balance	$ 2,248,432		$ 2,248,432		$ 2,507,514
Principal Balance, collateral assets	2,892,807		2,892,807		3,151,889
Book Value	2,248,307		2,248,307		2,505,417
Book Value, collateral assets	2,892,807		$ 2,892,807		$ 3,151,889
Wtd. Avg. Yield/Cost, loan obligation			1.53%		1.79%
Wtd. Avg. Yield/Cost, collateral assets			3.03%		2.99%
Interest expense on debt	40,600	$ 44,500	$ 123,900	$ 127,600
2021 FL4 Senior Collateralized Loan Obligation | Securitized debt obligations, net
Debt Instrument [Line Items]
Count | loan			1		1
Principal Balance	785,453		$ 785,453		$ 803,750
Book Value	785,371		$ 785,371		$ 801,800
Wtd. Avg. Yield/Cost, loan obligation			1.40%		1.70%
2021 FL4 Underlying Collateral Assets | Securitized debt obligations, net
Debt Instrument [Line Items]
Count | loan			25		26
Principal Balance, collateral assets	981,703		$ 981,703		$ 1,000,000
Book Value, collateral assets	981,703		$ 981,703		$ 1,000,000
Wtd. Avg. Yield/Cost, collateral assets			3.26%		3.28%
2020 FL3 Senior Collateralized Loan Obligation | Securitized debt obligations, net
Debt Instrument [Line Items]
Count | loan			1		1
Principal Balance	659,495		$ 659,495		$ 714,352
Book Value	659,494		$ 659,494		$ 714,352
Wtd. Avg. Yield/Cost, loan obligation			1.86%		2.18%
2020 FL3 Underlying Collateral Assets | Securitized debt obligations, net
Debt Instrument [Line Items]
Count | loan			14		15
Principal Balance, collateral assets	850,745		$ 850,745		$ 905,602
Book Value, collateral assets	850,745		$ 850,745		$ 905,602
Wtd. Avg. Yield/Cost, collateral assets			3.06%		2.87%
2020 FL2 Senior Collateralized Loan Obligation | Securitized debt obligations, net
Debt Instrument [Line Items]
Count | loan			1		1
Principal Balance	803,484		$ 803,484		$ 989,412
Book Value	803,442		$ 803,442		$ 989,265
Wtd. Avg. Yield/Cost, loan obligation			1.38%		1.57%
2020 FL2 Underlying Collateral Assets | Securitized debt obligations, net
Debt Instrument [Line Items]
Count | loan			14		15
Principal Balance, collateral assets	1,060,359		$ 1,060,359		$ 1,246,287
Book Value, collateral assets	$ 1,060,359		$ 1,060,359		$ 1,246,287
Wtd. Avg. Yield/Cost, collateral assets			2.82%		2.85%