| Standard label: | Share-based Payment Arrangement, Performance Shares, Outstanding Activity [Table Text Block] |
| Name: | us-gaap:ShareBasedCompensationPerformanceSharesAwardOutstandingActivityTableTextBlock |
| Documentation: | Tabular disclosure of the number and weighted-average grant date fair value for outstanding performance shares. |
| Object type: | cm:Level3TextBlock |
| Data type: | Text Block (HTML) (nonnum:textBlockItemType) |
| Period type: | For Period (duration) |
| Balance type: | (no balance type) |
| Abstract: | false |
| Workiva Wdesk Taxonomy Analyzer: | us-gaap:ShareBasedCompensationPerformanceSharesAwardOutstandingActivityTableTextBlock |
| Label | Role | Language |
| Share-based Payment Arrangement, Performance Shares, Outstanding Activity [Table Text Block] | http://www.xbrl.org/2003/role/label | en-US |
| Reference | Role | Topic |
| FASB Accounting Standards Codification 718 10 50 2 (c) | http://fasb.org/us-gaap/role/ref/legacyRef | 718 |