v3.26.1
Cover Page - USD ($)
12 Months Ended
Dec. 31, 2025
Mar. 24, 2026
Jun. 30, 2025
Cover [Abstract]      
Document Type 10-K    
Document Annual Report true    
Document Period End Date Dec. 31, 2025    
Current Fiscal Year End Date --12-31    
Document Transition Report false    
Entity File Number 000-54687    
Entity Registrant Name KBS REAL ESTATE INVESTMENT TRUST III, INC.    
Entity Incorporation, State or Country Code MD    
Entity Tax Identification Number 27-1627696    
Entity Address, Address Line One 800 Newport Center Drive    
Entity Address, Address Line Two Suite 700    
Entity Address, City or Town Newport Beach    
Entity Address, State or Province CA    
Entity Address, Postal Zip Code 92660    
City Area Code 949    
Local Phone Number 417-6500    
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Interactive Data Current Yes    
Entity Filer Category Non-accelerated Filer    
Entity Small Business false    
Entity Emerging Growth Company false    
ICFR Auditor Attestation Flag false    
Document Financial Statement Error Correction false    
Entity Shell Company false    
Entity Public Float     $ 0
Entity Common Stock, Shares Outstanding   148,516,246  
Amendment Flag false    
Document Fiscal Period Focus FY    
Entity Central Index Key 0001482430    
Document Fiscal Year Focus 2025