v3.23.3
Portfolio Investments - Significant Unobservable Inputs for Level 3 Investments (Details)
$ in Thousands
Sep. 30, 2023
USD ($)
Sep. 30, 2022
USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value $ 2,892,420 $ 2,494,111
Senior secured debt    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value 2,501,385 2,166,409
Debt investments in the JVs    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value 162,673 146,533
Level 3    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value 2,619,912 2,169,475
Level 3 | Senior secured debt    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value 2,292,691 1,910,606
Level 3 | Senior secured debt | Valuation, Market Approach | Measurement Input, Market Yield    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value $ 1,904,140 $ 1,599,148
Level 3 | Senior secured debt | Valuation, Market Approach | Measurement Input, Market Yield | Minimum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment Company, Investment Owned, Measurement Input 0.090 0.090
Level 3 | Senior secured debt | Valuation, Market Approach | Measurement Input, Market Yield | Maximum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment Company, Investment Owned, Measurement Input 0.320 0.300
Level 3 | Senior secured debt | Valuation, Market Approach | Measurement Input, Market Yield | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment Company, Investment Owned, Measurement Input 0.147 0.137
Level 3 | Senior secured debt | Valuation, Enterprise Value | Measurement Input, EBITDA Multiple    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value $ 64,802 $ 14,333
Level 3 | Senior secured debt | Valuation, Enterprise Value | Measurement Input, EBITDA Multiple | Minimum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment Company, Investment Owned, Measurement Input 3.0 5.0
Level 3 | Senior secured debt | Valuation, Enterprise Value | Measurement Input, EBITDA Multiple | Maximum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment Company, Investment Owned, Measurement Input 6.0 7.0
Level 3 | Senior secured debt | Valuation, Enterprise Value | Measurement Input, EBITDA Multiple | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment Company, Investment Owned, Measurement Input 4.6 6.0
Level 3 | Senior secured debt | Valuation, Transaction Precedent | Measurement Input, Transaction Price    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value $ 33,816  
Level 3 | Senior secured debt | Valuation, Broker Quotations | Measurement Input, Transaction Price    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value   $ 297,125
Level 3 | Senior secured debt | Valuation, Broker Quotations | Measurement Input, Broker Quoted Price    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value 289,933  
Level 3 | Subordinated Debt | Valuation, Market Approach | Measurement Input, Market Yield    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value $ 22,881 $ 12,855
Level 3 | Subordinated Debt | Valuation, Market Approach | Measurement Input, Market Yield | Minimum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment Company, Investment Owned, Measurement Input 0.100 0.100
Level 3 | Subordinated Debt | Valuation, Market Approach | Measurement Input, Market Yield | Maximum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment Company, Investment Owned, Measurement Input 0.220 0.190
Level 3 | Subordinated Debt | Valuation, Market Approach | Measurement Input, Market Yield | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment Company, Investment Owned, Measurement Input 0.112 0.138
Level 3 | Subordinated Debt | Valuation, Broker Quotations | Measurement Input, Broker Quoted Price    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value $ 4,170  
Level 3 | Debt investments in the JVs | Valuation, Enterprise Value    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value 162,673 $ 146,533
Level 3 | Equity Securities, Preferred & Common | Valuation, Enterprise Value | Measurement Input, Revenue Multiple    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value $ 32,318 $ 61,693
Level 3 | Equity Securities, Preferred & Common | Valuation, Enterprise Value | Measurement Input, Revenue Multiple | Minimum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment Company, Investment Owned, Measurement Input 0.4 0.4
Level 3 | Equity Securities, Preferred & Common | Valuation, Enterprise Value | Measurement Input, Revenue Multiple | Maximum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment Company, Investment Owned, Measurement Input 3.2 10.1
Level 3 | Equity Securities, Preferred & Common | Valuation, Enterprise Value | Measurement Input, Revenue Multiple | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment Company, Investment Owned, Measurement Input 0.5 4.3
Level 3 | Equity Securities, Preferred & Common | Valuation, Enterprise Value | Measurement Input, EBITDA Multiple    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value $ 103,661 $ 36,913
Level 3 | Equity Securities, Preferred & Common | Valuation, Enterprise Value | Measurement Input, EBITDA Multiple | Minimum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment Company, Investment Owned, Measurement Input 1.7 3.0
Level 3 | Equity Securities, Preferred & Common | Valuation, Enterprise Value | Measurement Input, EBITDA Multiple | Maximum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment Company, Investment Owned, Measurement Input 15.1 20.0
Level 3 | Equity Securities, Preferred & Common | Valuation, Enterprise Value | Measurement Input, EBITDA Multiple | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment Company, Investment Owned, Measurement Input 8.8 11.4
Level 3 | Equity Securities, Preferred & Common | Valuation, Enterprise Value | Measurement Input, Asset Multiple    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value $ 1,097 $ 3
Level 3 | Equity Securities, Preferred & Common | Valuation, Enterprise Value | Measurement Input, Asset Multiple | Minimum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment Company, Investment Owned, Measurement Input 1.0 0.9
Level 3 | Equity Securities, Preferred & Common | Valuation, Enterprise Value | Measurement Input, Asset Multiple | Maximum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment Company, Investment Owned, Measurement Input 1.4 1.1
Level 3 | Equity Securities, Preferred & Common | Valuation, Enterprise Value | Measurement Input, Asset Multiple | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment Company, Investment Owned, Measurement Input 1.4 1.0
Level 3 | Equity Securities, Preferred & Common | Valuation, Transaction Precedent | Measurement Input, Transaction Price    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value $ 421 $ 872