| Standard label: | Open Option Contracts Written [Table] |
| Name: | us-gaap:OpenOptionContractsWrittenTable |
| Documentation: | Listing of open option contracts written. |
| Object type: | cm:Table |
| Data type: | Text/String (xbrli:stringItemType) |
| Period type: | For Period (duration) |
| Balance type: | (no balance type) |
| Abstract: | true |
| Workiva Wdesk Taxonomy Analyzer: | us-gaap:OpenOptionContractsWrittenTable |
| Label | Role | Language |
| Open Option Contracts Written [Table] | http://www.xbrl.org/2003/role/label | en-US |
| Reference | Role | Topic |
| FASB Accounting Standards Codification 946 320 S99 3 (SX 210.12-12B) | http://fasb.org/us-gaap/role/ref/legacyRef | 946 |