| Standard label: | Increase (Decrease) in Unearned Premiums |
| Name: | us-gaap:IncreaseDecreaseInUnearnedPremiums |
| Documentation: | Amount of increase (decrease) unearned premiums written. Excludes portion of unearned premiums amortized into income. |
| Object type: | cm:Concept |
| Data type: | Monetary (xbrli:monetaryItemType) |
| Period type: | For Period (duration) |
| Balance type: | Debit |
| Abstract: | false |
| Workiva Wdesk Taxonomy Analyzer: | us-gaap:IncreaseDecreaseInUnearnedPremiums |
| Label | Role | Language |
| Increase (Decrease) in Unearned Premiums | http://www.xbrl.org/2003/role/label | en-US |
| Reference | Role | Topic |
| FASB Accounting Standards Codification 230 10 45 28 (a) | http://fasb.org/us-gaap/role/ref/legacyRef | 230 |
| Part Of Roll Up: |
| us-gaap:IncreaseDecreaseInInsuranceLiabilities |