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 |