v3.26.1
Cover - shares
 3 Months Ended
Mar. 31, 2026
May 11, 2026
Document Information [Line Items]    
Document Type 10-Q  
Document Quarterly Report true  
Document Transition Report false  
Entity Interactive Data Current Yes  
Amendment Flag false  
Document Period End Date Mar. 31, 2026  
Document Fiscal Year Focus 2026  
Document Fiscal Period Focus Q1  
Entity Information [Line Items]    
Entity Registrant Name PLUM ACQUISITION CORP. III  
Entity Central Index Key 0001845550  
Entity File Number 001-40677  
Entity Tax Identification Number 98-1581691  
Entity Incorporation, State or Country Code E9  
Current Fiscal Year End Date --12-31  
Entity Current Reporting Status Yes  
Entity Shell Company true  
Entity Filer Category Non-accelerated Filer  
Entity Small Business true  
Entity Emerging Growth Company true  
Entity Ex Transition Period false  
Entity Contact Personnel [Line Items]    
Entity Address, Address Line One 2021 Fillmore St., #2089  
Entity Address, City or Town San Francisco  
Entity Address, State or Province CA  
Entity Address, Postal Zip Code 94115  
Entity Phone Fax Numbers [Line Items]    
City Area Code +1 (929)  
Local Phone Number 529-7129  
Class A Ordinary Shares    
Entity Listings [Line Items]    
Entity Common Stock, Shares Outstanding   907,486
Class B Ordinary Shares    
Entity Listings [Line Items]    
Entity Common Stock, Shares Outstanding   7,062,500