cm:Concept: us-gaap:RestrictedStockValueSharesIssuedNetOfTaxWithholdings
| Restricted Stock, Value, Shares Issued Net of Tax Withholdings |
| us-gaap:RestrictedStockValueSharesIssuedNetOfTaxWithholdings |
| Value, after value of shares used to satisfy grantee's tax withholding obligation for award under share-based payment arrangement, of restricted shares issued. Excludes cash used to satisfy grantee's tax withholding obligation. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Credit |
| false |
| us-gaap:RestrictedStockValueSharesIssuedNetOfTaxWithholdings |