cm:Concept: us-gaap:AdjustmentsToAdditionalPaidInCapitalIncomeTaxDeficiencyFromShareBasedCompensation
| Adjustments to Additional Paid in Capital, Income Tax Deficiency from Share-based Compensation |
| us-gaap:AdjustmentsToAdditionalPaidInCapitalIncomeTaxDeficiencyFromShareBasedCompensation |
| Amount of decrease in additional paid in capital (APIC) resulting from a tax deficiency associated with a share-based compensation plan other than an employee stock ownership plan (ESOP). |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Debit |
| false |
| us-gaap:AdjustmentsToAdditionalPaidInCapitalIncomeTaxDeficiencyFromShareBasedCompensation |