| INVESTMENTS - Investments Classified by Contractual Maturity Date (Details) - USD ($) $ in Thousands | Sep. 30, 2024 | Sep. 30, 2023 | [2] | |||||
|---|---|---|---|---|---|---|---|---|
| Investments, Debt and Equity Securities [Abstract] | ||||||||
| 2025 | $ 16,322 | |||||||
| 2026 | 160,366 | |||||||
| 2027 | 227,287 | |||||||
| 2028 | 193,374 | |||||||
| 2029 | 78,697 | |||||||
| Thereafter | 20,000 | |||||||
| Total contractual repayments | 696,046 | |||||||
| Adjustments to cost basis of debt investments | (1,421) | |||||||
| Investments in equity securities | 76,386 | |||||||
| Investment owned, at cost | 771,011 | [1] | $ 722,269 | |||||
| Debt investments with maturity dates prior to period end | $ 200 | |||||||
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| X | ||||||||||
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- Definition Debt Investments With Maturity Dates Prior To Period End, Amount No definition available. 
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| X | ||||||||||
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- Definition Principal Repayment And Maturity Of Investments, No definition available. 
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| X | ||||||||||
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- Definition Principal Repayment And Maturity Of Investments, Adjustments to Cost Basis of Debt Investments No definition available. 
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| X | ||||||||||
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- Definition Principal Repayment And Maturity Of Investments, After Year Four No definition available. 
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| X | ||||||||||
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- Definition Principal Repayment And Maturity Of Investments, Year Five No definition available. 
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| X | ||||||||||
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- Definition Principal Repayment And Maturity Of Investments, Year Four No definition available. 
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| X | ||||||||||
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- Definition Principal Repayment And Maturity Of Investments, Year One No definition available. 
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| X | ||||||||||
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- Definition Principal Repayment And Maturity Of Investments, Year Three No definition available. 
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| X | ||||||||||
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- Definition Principal Repayment And Maturity Of Investments, Year Two No definition available. 
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| X | ||||||||||
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- Definition Cost of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). Excludes equity method investment and investment in equity security without readily determinable fair value. Reference 1: http://www.xbrl.org/2003/role/disclosureRef 
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| X | ||||||||||
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- Definition Cost of the investment. Reference 1: http://www.xbrl.org/2003/role/exampleRef 
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| X | ||||||||||
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- References No definition available. 
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