v3.25.2
Summary of Significant Accounting Policies - Additional Information (Details)
 3 Months Ended 6 Months Ended
Mar. 31, 2025
USD ($)
Mar. 01, 2025
USD ($)
shares
Jul. 26, 2024
USD ($)
$ / shares
shares
Jun. 30, 2025
USD ($)
shares
Jun. 30, 2024
USD ($)
Jun. 30, 2025
USD ($)
Segment
shares
Jun. 30, 2024
USD ($)
Dec. 31, 2024
USD ($)
Mar. 31, 2024
USD ($)
Dec. 31, 2023
USD ($)
Apr. 30, 2021
shares
Significant Accounting Policies [Line Items]                      
Shares issued for directors and employee stock plans (in shares) | shares     1,380,000                
Sales price per share (in dollars per share) | $ / shares     $ 25                
Issuance of common stock     $ 34,500,000     $ 432,000 $ 115,000        
Provision for credit losses on loans       $ 650,000 $ 0 13,813,000 0        
Allowance for credit loss $ 34,567,000     34,798,000 16,152,000 34,798,000 16,152,000 $ 16,552,000 $ 16,037,000 $ 15,685,000  
Estimated accretable interest income           59,800,000          
Merger-related expenses           64,700,000          
Stock repurchase program, number of shares authorized to be repurchased (in shares) | shares                     375,388
Stock repurchase program, percent of stock outstanding                     5.00%
Securities held to maturity, Accrued interest receivable       2,000,000   2,000,000   $ 2,000,000      
Shares issued for directors and employee stock plans       $ 261,000 $ 25,000 $ 433,000 $ 115,000        
Number of days individually evaluation           60 days          
Stock repurchased during period, shares (in shares) | shares           0          
Number of reportable segments | Segment           1          
ASU 2023-07                      
Significant Accounting Policies [Line Items]                      
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]       true   true          
Change in Accounting Principle, Accounting Standards Update, Adoption Date       Dec. 31, 2024   Dec. 31, 2024          
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]       true   true          
Fentura Financial, Inc. [Member]                      
Significant Accounting Policies [Line Items]                      
Shares issued for directors and employee stock plans (in shares) | shares   6,070,836                  
Cash price 2,200,000                    
Common stock purchased   $ 57,807                  
Shares issued for directors and employee stock plans   192,800,000                  
Non-PCD Loans [Member]                      
Significant Accounting Policies [Line Items]                      
Provision for credit losses on loans   12,000,000                  
Loans purchased           $ 51,600,000          
Merger PCD loans   $ 1,300,000,000                  
PCD Loans [Member]                      
Significant Accounting Policies [Line Items]                      
Allowance for credit loss       $ 4,900,000   4,900,000          
Loans purchased           $ 13,100,000          
Directors' Stock Purchase Plan [Member]                      
Significant Accounting Policies [Line Items]                      
Shares issued for directors and employee stock plans (in shares) | shares       7,005   10,306          
Shares issued for directors and employee stock plans       $ 203,000   $ 320,000          
Employee Stock Purchase Plan [Member]                      
Significant Accounting Policies [Line Items]                      
Shares issued for directors and employee stock plans (in shares) | shares       2,397   4,611          
Shares issued for directors and employee stock plans       $ 58,000   $ 113,000          
FETM Shares Retired [Member]                      
Significant Accounting Policies [Line Items]                      
Shares issued for directors and employee stock plans (in shares) | shares   6,750                  
Shares issued for directors and employee stock plans $ 215,000