cm:Concept: us-gaap:WeightedAverageNumberOfSharesEmployeeStockOwnershipPlanSharesNotCommittedToBeReleased
| Weighted Average Number of Shares, Employee Stock Ownership Plan Shares Not Committed to be Released |
| us-gaap:WeightedAverageNumberOfSharesEmployeeStockOwnershipPlanSharesNotCommittedToBeReleased |
| Number of employee stock ownership plan (ESOP) shares that have not been committed to be released determined by relating the portion of time within a reporting period that these shares have been outstanding to the total time in that period. |
| cm:Concept |
| Shares (xbrli:sharesItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:WeightedAverageNumberOfSharesEmployeeStockOwnershipPlanSharesNotCommittedToBeReleased |