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Summary of Significant Accounting Policies Summary of Significant Account Policies (Debt Issuance Costs) (Details) - USD ($) $ in Millions | Dec. 31, 2016 | Dec. 31, 2015
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Debt Instrument [Line Items] |  |
Debt issuance costs | $ 1.6 |
OneBeacon |  |
Debt Instrument [Line Items] |  |
Debt issuance costs |  | $ 1.9

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition Amount, before accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 45 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28555-108399 + Details
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- Details
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