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Summary of Significant Accounting Policies (Details) |  |  | 12 Months Ended
--- | --- | --- | ---
Mar. 31, 2012 state | Mar. 31, 2012 OneBeacon Ltd. | Dec. 31, 2011 OneBeacon Ltd. | Dec. 31, 2011 Tuckerman Fund company
Basis of Presentation |  |  |  |
Ownership percentage in outstanding common shares |  | 75.20% | 75.50% |
Number of small manufacturing companies owned by the Tuckerman Fund I from whom the entity received shares |  |  |  | 2
Number of states in which Esurance insurance directly writes insurance | 30 |  |  |

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- Details
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- Definition Represents the number of manufacturing companies from whom the entity received the shares. + References No definition available. + Details
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- Definition Represents the number of states in which insurance is directly written to customers. + References No definition available. + Details
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