| Standard label: | Open Option Contracts Written Type [Domain] |
| Name: | us-gaap:OpenOptionContractsWrittenTypeDomain |
| Documentation: | This domain is used for open option contracts written table to separate the put options from the call options. |
| 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:OpenOptionContractsWrittenTypeDomain |
| Label | Role | Language |
| Open Option Contracts Written Type [Domain] | http://www.xbrl.org/2003/role/label | en-US |
| Reference | Role | Topic |
| FASB Accounting Standards Codification 946 320 S99 3 (SX 210.12-12B.1) | http://fasb.org/us-gaap/role/ref/legacyRef | 946 |