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Third Party Reinsurance (Sirius Group) (Details) (USD $) In Millions, unless otherwise specified | Jun. 30, 2013 | Mar. 31, 2013 | Dec. 31, 2012 | Jun. 30, 2012 | Mar. 31, 2012 | Dec. 31, 2011
--- | --- | --- | --- | --- | --- | ---
Reinsurance [Line Items] |  |  |  |  |  |  |
Reinsurance recoverable on paid losses | $ 16.1 |  |  | $ 17.9 |  |  |
Reinsurance recoverable on unpaid losses | 388.6 |  | 410.8 | 429.1 | 2,369.4 | 2,465.4 | 2,507.3
Sirius |  |  |  |  |  |  |
Reinsurance [Line Items] |  |  |  |  |  |  |
Reinsurance recoverable on paid losses | 13.3 |  |  |  |  |  |
Reinsurance recoverable on unpaid losses | 306.8 |  |  |  |  |  |
Berkshire Hathaway [Member] | Sirius |  |  |  |  |  |  |
Reinsurance [Line Items] |  |  |  |  |  |  |
Reinsurance recoverables | 56.3 |  |  |  |  |  |
Percentage of total paid and unpaid reinsurance recoverables | 18.00% |  |  |  |  |  |
Percentage Collateralized | 0.00% |  |  |  |  |  |
Swiss Re Group | Sirius |  |  |  |  |  |  |
Reinsurance [Line Items] |  |  |  |  |  |  |
Reinsurance recoverables | 34.0 |  |  |  |  |  |
Percentage of total paid and unpaid reinsurance recoverables | 11.00% |  |  |  |  |  |
Percentage Collateralized | 0.00% |  |  |  |  |  |
Olympus | Sirius |  |  |  |  |  |  |
Reinsurance [Line Items] |  |  |  |  |  |  |
Reinsurance recoverables | 25.0 | [1] |  |  |  |  |
Percentage of total paid and unpaid reinsurance recoverables | 8.00% | [1] |  |  |  |  |
Percentage Collateralized | 100.00% | [1] |  |  |  |  |
Lloyds of London | Sirius |  |  |  |  |  |  |
Reinsurance [Line Items] |  |  |  |  |  |  |
Reinsurance recoverables | 16.1 | [2] |  |  |  |  |
Percentage of total paid and unpaid reinsurance recoverables | 5.00% | [2] |  |  |  |  |
Percentage Collateralized | 16.00% | [2] |  |  |  |  |
International Medical Insurance Co Ltd [Member] | Sirius |  |  |  |  |  |  |
Reinsurance [Line Items] |  |  |  |  |  |  |
Reinsurance recoverables | $ 12.2 |  |  |  |  |  |
Percentage of total paid and unpaid reinsurance recoverables | 4.00% |  |  |  |  |  |
Michigan Catastorphic Claims Association [Member] | Sirius |  |  |  |  |  |  |
Reinsurance [Line Items] |  |  |  |  |  |  |
Percentage Collateralized | 31.00% |  |  |  |  |  |
[1] | Non-U.S. insurance entity. The balance is fully collateralized through trust agreements or funds held.
[2] | Represents the total of reinsurance recoverables due to Sirius Group from all Lloyds Syndicates.

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- Definition The portion of reinsurance receivables representing the aggregate amount of estimated amounts due as of the balance sheet date from another insurer; also called reinsurance recoverables or unpaid losses recoverable, that are expected based upon statistical projections of incurred claims and claims settlement expenses which have not yet been reported to the insurer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 6 -Article 7 Reference 2: 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 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 310 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6485522&loc=d3e21409-158489 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 113 -Paragraph 14, 15 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. + Details
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- Definition Receivables currently due from reinsurers for ceded claims paid. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 605 -Section 50 -Paragraph 1 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=6486672&loc=d3e27261-158547 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 6 -Article 7 Reference 3: 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 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 310 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6485522&loc=d3e21409-158489 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.6) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 113 -Paragraph 14, 15 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. + Details
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- Definition The known and estimated amount recoverable as of the balance sheet date from reinsurers for claims paid or incurred by the ceding insurer and associated claims settlement expenses, including estimated amounts for claims incurred but not reported, and policy benefits, net of any related valuation allowance. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 6 -Article 7 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 20 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6480758&loc=d3e6824-158387 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.(a),6) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 113 -Paragraph 14, 16, 27, 113 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. + Details
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- Definition Represents the percentage of a top reinsurer's recoverable amounts that are collateralized. + References No definition available. + Details
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- Definition The respective third party reinsurers' percentage share of the total paid and unpaid reinsurance recoverables. + References No definition available. + Details
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