v3.26.1
Cover - USD ($)
$ in Millions
 12 Months Ended
Sep. 30, 2025
Jul. 01, 2026
Mar. 31, 2025
Document Information [Line Items]      
Document Type 10-K/A    
Amendment Flag true    
Document Period End Date Sep. 30, 2025    
Document Fiscal Year Focus 2025    
Document Fiscal Period Focus FY    
Entity Registrant Name PENNANTPARK INVESTMENT CORPORATION    
Entity Central Index Key 0001383414    
Current Fiscal Year End Date --09-30    
Document Annual Report true    
Document Transition Report false    
Entity File Number 814-00736    
Entity Tax Identification Number 20-8250744    
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Interactive Data Current Yes    
Entity Filer Category Accelerated Filer    
Entity Small Business false    
Entity Emerging Growth Company false    
Entity Shell Company false    
Document Financial Statement Error Correction [Flag] false    
ICFR Auditor Attestation Flag true    
Entity Incorporation, State or Country Code MD    
Entity Address, Address Line One 1691 Michigan Avenue    
Entity Address, City or Town Miami Beach    
Entity Address, State or Province FL    
Entity Address, Postal Zip Code 33139    
City Area Code 786    
Local Phone Number 297-9500    
Title of 12(b) Security Common Stock, par value $0.001 per share    
Trading Symbol PNNT    
Security Exchange Name NYSE    
Entity Public Float     $ 443.6
Entity Common Stock, Shares Outstanding   65,296,094  
Documents Incorporated by Reference [Text Block] Documents Incorporated by Reference: Portions of the Registrant’s Proxy Statement relating to the Registrant’s 2026 Annual Meeting of Stockholders to be filed not later than 120 days after the end of the fiscal year covered by this Annual Report on Form
10-K
are incorporated by reference into Part III of this Report. 		   
Amendment Description PennantPark Investment Corporation, a Maryland corporation, or together with its subsidiaries, where applicable, or the Company, which may also be referred to as “we,” “us” or “our,” is filing this Amendment No. 2, or this Amendment, to our Annual Report on Form 10-K for the fiscal year ended September 30, 2025, or the Form 10-K, which was initially filed with the Securities and Exchange Commission, or the SEC, on November 24, 2025. We are filing this Amendment to provide audited consolidated financial statements for our investment in an unconsolidated portfolio company, AKW Holdings Limited (“AKW”), as of December 31, 2025 and for the year ended December 31, 2025 and unaudited consolidated financial statements for our investment in AKW as of December 31, 2024 and for each of the years in the two-year period ended December 31, 2024 (as Exhibit 99.5). We have determined that this unconsolidated portfolio company has met the conditions of a significant subsidiary under Rule 1-02(w) of Regulation S-X for which we are required, pursuant to Rule 3-09 of Regulation S-X, to provide separate financial statements as exhibits to the Form 10-K. In accordance with Rule 3-09(b)(1), the separate audited and unaudited consolidated financial statements of AKW are being filed as an amendment to the Form 10-K. This Amendment also includes the filing of new Exhibits 31.1, 31.2, 32.1 and 32.2, certifications of our Chief Executive Officer and Chief Financial Officer, pursuant to Rule 13a-14(a) and (b) of the Securities Exchange Act of 1934, as amended. Except as described above, no other changes have been made to the Form 10-K. This Amendment does not reflect subsequent events that may have occurred after the original filing date of the Form 10-K or modify or update in any way disclosures made in the Form 10-K, except as required to reflect the revisions discussed above. Among other things, forward-looking statements made in the Form 10-K have not been revised to reflect events that occurred or facts that became known to us after filing of the Form 10-K, and such forward-looking statements should be read in their historical context. Furthermore, this Amendment should be read in conjunction with the Form 10-K and with our subsequent filings with the SEC.