| Standard label: | Surety Product Line [Member] |
| Name: | us-gaap:SuretySegmentMember |
| Documentation: | Contract providing insurance coverage for guarantee of performance. |
| 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:SuretySegmentMember |
| Label | Role | Language |
| Surety Product Line [Member] | http://www.xbrl.org/2003/role/label | en-US |
| Reference | Role | Topic |
| FASB Accounting Standards Codification 944 40 55 9C (a) | http://www.xbrl.org/2009/role/commonPracticeRef | 944 |