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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

X

- Definition

The parent entity's interest in net assets of the subsidiary, expressed as a percentage.

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- Definition

Represents the number of manufacturing companies from whom the entity received the shares.

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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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