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Third Party Reinsurance (Narrative) (Details) - USD ($) $ in Millions | 3 Months Ended |
--- | --- | ---
Mar. 31, 2016 | Dec. 31, 2015
Reinsurance Retention Policy [Line Items] |  |
Reinsurance recoverable on paid losses | $ 16.6 | $ 7.5
Reinsurance recoverable on unpaid losses | 150.9 | 186.5
OneBeacon [Member] |  |
Reinsurance Retention Policy [Line Items] |  |
Reinsurance recoverable on paid losses | 16.6 | 7.5
Reinsurance recoverable on unpaid losses | $ 150.4 | $ 186.0
OneBeacon [Member] |  |
Reinsurance Retention Policy [Line Items] |  |
Percentage of Quota Share Reinsurance Agreement | 50.00% |

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- Definition Amount after valuation allowance of reinsurance recoverables on paid losses. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 310 -Section 45 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=6485522&loc=d3e21412-158489 + Details
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- Definition Amount after valuation allowance of reinsurance recoverables for losses reported to the ceding insurer but not yet paid, amounts expected of incurred losses and settlement expenses, which have not yet been reported to the ceding insurer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 310 -Section 45 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=6485522&loc=d3e21412-158489 + Details
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- Definition Represents the percentage ceded under quota share reinsurance agreement. + References No definition available. + Details
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