Investments - Additional Information (Details) $ in Thousands		1 Months Ended	12 Months Ended
	Jul. 26, 2023 USD ($)	Oct. 31, 2024 USD ($)	Sep. 30, 2025 USD ($) Portfolio	Sep. 30, 2024 USD ($) Portfolio	Sep. 30, 2023 USD ($)	Jul. 21, 2025 USD ($)	Dec. 23, 2024 USD ($)	Aug. 28, 2024 USD ($)	Mar. 31, 2022 USD ($)
Schedule Of Investments [Line Items]
Purchases of investments, including PIK interest			$ 754,300	$ 784,200	$ 279,900
Sales and repayments of investments			810,400	555,400	$ 418,600
Total assets			$ 1,349,554	$ 1,389,086
Number of portfolio companies consisted of debt investments | Portfolio			109	102
Credit facility payable			$ 425,477	$ 460,361
Subordinated Notes
Schedule Of Investments [Line Items]
Percentage of capital ownership in each of outstanding subordinated notes and equity interests			55.80%	60.50%
Investments			$ 140,300	$ 115,900
Equity Interests in PSLF
Schedule Of Investments [Line Items]
Percentage of capital ownership in each of outstanding subordinated notes and equity interests			44.20%	39.50%
Investments			$ 82,400	$ 67,400
Capital contribution		$ 26,300
Equity Interests in PSLF | Pantheon
Schedule Of Investments [Line Items]
Remaining commitments to fund			5,000	19,900
Equity Interests in PSLF | Pantheon Funding I
Schedule Of Investments [Line Items]
Remaining commitments to fund			7,100	28,500
PSLF
Schedule Of Investments [Line Items]
Total assets			1,315,447	1,073,352
Fair value of largest investment in a single portfolio company			24,800	25,100
Fair value of investment in five largest portfolio company			121,400	109,900
Credit facility payable			$ 99,600	247,600
PSLF | PSLF Subsidiary
Schedule Of Investments [Line Items]
Asset backed debt									$ 304,000
Asset backed debt, transfer of assets, description			On the closing date of the transaction, in consideration of PSLF’s transfer to PennantPark CLO IV, LLC. of the initial closing date loan portfolio, which included loans distributed to PSLF by certain of its wholly owned subsidiaries and us, PennantPark CLO IV, LLC. transferred to PSLF 100% of the Preferred Shares of PennantPark CLO IV, LLC. and 100% of the Subordinated Notes issued by PennantPark CLO IV, LLC.
PSLF | PSLF Subsidiary | Senior Secured Revolving Credit Facility
Schedule Of Investments [Line Items]
Credit facility payable			$ 400,000					$ 325,000
Credit facility interest rate description			interest at SOFR (or an alternative risk-free interest rate index) plus 225 basis points during the investment period and is subject to leverage and borrowing base restrictions.
Interest rate at basis points			225.00%
PSLF | Pantheon
Schedule Of Investments [Line Items]
Remaining commitments to fund			$ 8,200	32,600
PSLF | Pantheon Funding I
Schedule Of Investments [Line Items]
Remaining commitments to fund			11,700	46,500
Pennant Park CLO X [Member]
Schedule Of Investments [Line Items]
Asset backed debt			328,000
Pennant Park CLO X [Member] | PSLF Subsidiary
Schedule Of Investments [Line Items]
Asset backed debt							$ 400,500
CLO VII
Schedule Of Investments [Line Items]
Asset backed debt			$ 246,000	$ 246,000
CLO VII | PSLF Subsidiary
Schedule Of Investments [Line Items]
Asset backed debt	$ 300,000
Private Placement [Member] | PSLF | PSLF and Pantheon Amendement [Member] | Maximum [Member] | LLC Agreement [Member]
Schedule Of Investments [Line Items]
Ownership interest percentage								87.50%
Private Placement [Member] | PSLF | PSLF and Pantheon Amendement [Member] | Minimum [Member] | LLC Agreement [Member]
Schedule Of Investments [Line Items]
Ownership interest percentage								25.00%
Class A-1a [Member] | Private Placement [Member] | Pennant Park CLO X [Member]
Schedule Of Investments [Line Items]
Investments Basis Spread Variable Rate			1.59%
Debt securitization			$ 30,000
Class A-1a [Member] | Private Placement [Member] | CLO VII
Schedule Of Investments [Line Items]
Debt securitization	$ 151,000
Class A-1W [Member] | Private Placement [Member] | Pennant Park CLO X [Member]
Schedule Of Investments [Line Items]
Debt securitization			40,000
Class A-2W [Member] | Private Placement [Member] | Pennant Park CLO X [Member]
Schedule Of Investments [Line Items]
Debt securitization			16,000
Class A-1 [Member] | Private Placement [Member] | Pennant Park CLO X [Member]
Schedule Of Investments [Line Items]
Debt securitization			$ 158,000
Class A1b [Member] | Private Placement [Member] | CLO VII
Schedule Of Investments [Line Items]
Interest rate at basis points	6.50%
Debt securitization	$ 20,000
Class A-2 [Member] | Private Placement [Member] | CLO VII
Schedule Of Investments [Line Items]
Investments Basis Spread Variable Rate	3.20%
Debt securitization	$ 12,000
Class B [Member] | Private Placement [Member] | Pennant Park CLO X [Member]
Schedule Of Investments [Line Items]
Investments Basis Spread Variable Rate			1.85%
Debt securitization			$ 28,000
Class B [Member] | Private Placement [Member] | CLO VII
Schedule Of Investments [Line Items]
Debt securitization	21,000
Class B (B-R) [Member] | CLO VII
Schedule Of Investments [Line Items]
Debt securitization						$ 21,000
Class C (C-R) [Member] | CLO VII
Schedule Of Investments [Line Items]
Debt securitization						$ 24,000
Class D (D-R) [Member] | CLO VII
Schedule Of Investments [Line Items]
Investments Basis Spread Variable Rate						2.30%
Debt securitization						$ 18,000
Class C [Member] | Private Placement [Member] | Pennant Park CLO X [Member]
Schedule Of Investments [Line Items]
Investments Basis Spread Variable Rate			2.40%
Debt securitization			$ 32,000
Class C [Member] | Private Placement [Member] | CLO VII
Schedule Of Investments [Line Items]
Debt securitization	24,000
Class D [Member] | Private Placement [Member] | Pennant Park CLO X [Member]
Schedule Of Investments [Line Items]
Debt securitization			$ 24,000
Class D [Member] | Private Placement [Member] | CLO VII
Schedule Of Investments [Line Items]
Debt securitization	$ 18,000
SOFR | Class A-1a [Member] | Private Placement [Member] | CLO VII
Schedule Of Investments [Line Items]
Investments Basis Spread Variable Rate	2.70%
SOFR | Class A-2W [Member] | Private Placement [Member] | Pennant Park CLO X [Member]
Schedule Of Investments [Line Items]
Investments Basis Spread Variable Rate			1.75%
SOFR | Class A-1 [Member] | Private Placement [Member] | Pennant Park CLO X [Member]
Schedule Of Investments [Line Items]
Investments Basis Spread Variable Rate			1.59%
SOFR | Class B [Member] | Private Placement [Member] | CLO VII
Schedule Of Investments [Line Items]
Investments Basis Spread Variable Rate	4.10%
SOFR | Class C (C-R) [Member] | CLO VII
Schedule Of Investments [Line Items]
Investments Basis Spread Variable Rate						2.00%
SOFR | Class D (D-R) [Member] | CLO VII
Schedule Of Investments [Line Items]
Investments Basis Spread Variable Rate						3.40%
SOFR | Class C [Member] | Private Placement [Member] | CLO VII
Schedule Of Investments [Line Items]
Investments Basis Spread Variable Rate	4.70%
SOFR | Class D [Member] | Private Placement [Member] | Pennant Park CLO X [Member]
Schedule Of Investments [Line Items]
Investments Basis Spread Variable Rate			3.85%
SOFR | Class D [Member] | Private Placement [Member] | CLO VII
Schedule Of Investments [Line Items]
Investments Basis Spread Variable Rate	7.00%