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Cover - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2024
Mar. 11, 2025
Jun. 30, 2024
Cover [Abstract]      
Document Type 10-K    
Document Annual Report true    
Document Period End Date Dec. 31, 2024    
Document Transition Report false    
Entity File Number 0-18415    
Entity Registrant Name Isabella Bank Corp    
Entity Incorporation, State or Country Code MI    
Entity Tax Identification Number 38-2830092    
Entity Address, Address Line One 401 North Main Street    
Entity Address, City or Town Mount Pleasant    
Entity Address, State or Province MI    
Entity Address, Postal Zip Code 48858    
City Area Code (989)    
Local Phone Number 772-9471    
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 true    
Entity Emerging Growth Company false    
ICFR Auditor Attestation Flag true    
Financial Statement Error Correction Flag false    
Entity Shell Company false    
Entity Public Float     $ 132,606
Entity Common Stock, Shares Outstanding   7,414,594  
Current Fiscal Year End Date --12-31