v3.26.1
Document and Entity Information - shares
6 Months Ended
Mar. 31, 2026
May 07, 2026
Cover [Abstract]    
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Mar. 31, 2026  
Document Fiscal Year Focus 2026  
Document Fiscal Period Focus Q2  
Entity Registrant Name PENNANTPARK INVESTMENT CORPORATION  
Entity Central Index Key 0001383414  
Current Fiscal Year End Date --09-30  
Document Quarterly Report true  
Document Transition Report false  
Entity File Number 814-00736  
Entity Tax Identification Number 20-8250744  
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  
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 Common Stock, Shares Outstanding   65,296,094