Agreements and Related Party Transactions - Additional Information (Details) - USD ($) $ in Thousands |
3 Months Ended | 9 Months Ended | |||||
|---|---|---|---|---|---|---|---|
Jun. 30, 2026 |
Jun. 30, 2025 |
Jun. 30, 2026 |
Jun. 30, 2025 |
Sep. 30, 2025 |
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| Related Party Transaction [Line Items] | |||||||
| Annual rate of base management fee | 1.00% | ||||||
| Base management fee | $ 6,400 | $ 5,900 | $ 19,600 | $ 16,800 | |||
| Base management fee calculation description | The base management fee is calculated based on the average adjusted gross assets at the end of the two most recently completed calendar quarters, and appropriately adjusted for any share issuances or repurchases during the current calendar quarter. | ||||||
| Incentive fee quarter hurdle rate | 1.75% | ||||||
| Incentive fee annual hurdle rate | 7.00% | ||||||
| Incentive fees on net investment income | 6,500 | 5,400 | $ 19,600 | 19,100 | |||
| Description of incentive fee on net investment income | We pay the Investment Adviser an incentive fee with respect to our Pre-Incentive Fee Net Investment Income in each calendar quarter as follows: (1) no incentive fee in any calendar quarter in which our Pre-Incentive Fee Net Investment Income does not exceed the hurdle rate of 1.75%, (2) 50% of our Pre-Incentive Fee Net Investment Income with respect to that portion of such Pre-Incentive Fee Net Investment Income, if any, that exceeds the hurdle rate but is less than 2.9167% in any calendar quarter (11.67% annualized) (we refer to this portion of our Pre-Incentive Fee Net Investment Income (which exceeds the hurdle but is less than 2.9167%) as the “catch-up,” which is meant to provide our Investment Adviser with 20% of our Pre-Incentive Fee Net Investment Income, as if a hurdle did not apply, if this net investment income exceeds 2.9167% in any calendar quarter), and (3) 20% of the amount of our Pre-Incentive Fee Net Investment Income, if any, that exceeds 2.9167% in any calendar quarter. | ||||||
| Incentive fee on capital gains percentage | 20.00% | ||||||
| Incentive fee on capital gains accrued | 0 | 0 | $ 0 | 0 | |||
| Incentive fee on unrealized and realized capital gains accrued | 0 | 0 | 0 | 0 | |||
| Administration fees | 1,350 | 1,200 | 3,750 | 3,600 | |||
| Due from affiliates | 0 | 0 | $ 700 | ||||
| Total Payable | 6,100 | 6,100 | 0 | ||||
| Other Related Party | |||||||
| Related Party Transaction [Line Items] | |||||||
| Net investment income | 0 | 0 | 0 | 0 | |||
| PennantPark Senior Secured Loan Fund I LLC | |||||||
| Related Party Transaction [Line Items] | |||||||
| Gain on Sale of Investments | 0 | (300) | (200) | (300) | |||
| Administration fees | [1] | 785 | 1,001 | 2,338 | 2,386 | ||
| Net investment income | 37,100 | 51,800 | 226,500 | 292,400 | |||
| Receivable from the Administraton | 200 | 200 | 300 | ||||
| Total Payable | 271,600 | 271,600 | $ 271,600 | ||||
| PennantPark Senior Secured Loan Fund II LLC | |||||||
| Related Party Transaction [Line Items] | |||||||
| Gain on Sale of Investments | 0 | 0 | (1,000) | 0 | |||
| Net investment income | 9,800 | 0 | 354,300 | 0 | |||
| Administrator | |||||||
| Related Party Transaction [Line Items] | |||||||
| Administration fees | $ 700 | $ 600 | 2,000 | $ 1,400 | |||
| Incentive Fee Payment Condition One | |||||||
| Related Party Transaction [Line Items] | |||||||
| Incentive fees on net investment income | $ 0 | ||||||
| Incentive Fee Payment Condition One | Maximum | |||||||
| Related Party Transaction [Line Items] | |||||||
| Incentive fee quarter hurdle rate | 1.75% | ||||||
| Incentive Fee Payment Condition Two | |||||||
| Related Party Transaction [Line Items] | |||||||
| Pre-incentive fee net investment income percentage | 50.00% | ||||||
| Incentive Fee Payment Condition Two | Maximum | |||||||
| Related Party Transaction [Line Items] | |||||||
| Incentive fee quarter hurdle rate | 2.9167% | ||||||
| Incentive fee annual hurdle rate | 11.67% | ||||||
| Incentive Fee Payment Condition Two | Minimum | |||||||
| Related Party Transaction [Line Items] | |||||||
| Incentive fee quarter hurdle rate | 2.9167% | ||||||
| Pre-incentive fee net investment income percentage | 20.00% | ||||||
| Incentive Fee Payment Condition Three | |||||||
| Related Party Transaction [Line Items] | |||||||
| Pre-incentive fee net investment income percentage | 20.00% | ||||||
| Incentive Fee Payment Condition Three | Minimum | |||||||
| Related Party Transaction [Line Items] | |||||||
| Incentive fee quarter hurdle rate | 2.9167% | ||||||
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