| Standard label: | Unionized Employees Concentration Risk [Member] |
| Name: | us-gaap:UnionizedEmployeesConcentrationRiskMember |
| Documentation: | Reflects the percentage that unionized employees, in either labor costs for the period or number of personnel as of the balance sheet date or on average for the period, are to a specified benchmark, such as total operating expenses, total labor costs, total corresponding number of personnel. Risk is the materially adverse effects of strikes and unfavorable contract negotiations with employees covered by collective bargaining arrangements. |
| Object type: | cm:Member |
| Data type: | [Member] (nonnum:domainItemType) |
| Period type: | For Period (duration) |
| Balance type: | (no balance type) |
| Abstract: | true |
| Workiva Wdesk Taxonomy Analyzer: | us-gaap:UnionizedEmployeesConcentrationRiskMember |
| Label | Role | Language |
| Unionized Employees Concentration Risk [Member] | http://www.xbrl.org/2003/role/label | en-US |
| Reference | Role | Topic |
| FASB Accounting Standards Codification 275 10 50 20 (a) | http://fasb.org/us-gaap/role/ref/legacyRef | 275 |