cm:Concept: us-gaap:GrandfatheredESOPExpenseRecognitionDividendsUsedByESOPForDebtService
       
          
          | Grandfathered ESOP Expense Recognition, Dividends Used by ESOP for Debt Service | 
       
       
          
          | us-gaap:GrandfatheredESOPExpenseRecognitionDividendsUsedByESOPForDebtService | 
       
       
          
          | For grandfathered ESOP shares acquired prior to January 1, 1993, the amount of ESOP dividends used to pay debt service by the sop. | 
       
       
          
          | cm:Concept | 
       
       
          
          | Monetary (xbrli:monetaryItemType) | 
       
       
          
          | For Period (duration) | 
       
       
          
          | Debit | 
       
       
          
          | false | 
       
       
          
          | us-gaap:GrandfatheredESOPExpenseRecognitionDividendsUsedByESOPForDebtService |