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Discontinued Operations (Details) (USD $) In Millions, unless otherwise specified | 3 Months Ended |  | 3 Months Ended |  |  |  | 3 Months Ended |  | 3 Months Ended |  | 3 Months Ended
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Mar. 31, 2013 | Mar. 31, 2012 | Dec. 31, 2012 | Mar. 31, 2013 Segment, Discontinued Operations | Mar. 31, 2012 Segment, Discontinued Operations | Dec. 31, 2012 Segment, Discontinued Operations | Mar. 31, 2013 Segment, Discontinued Operations OneBeacon Runoff Contract | Dec. 31, 2012 Segment, Discontinued Operations OneBeacon Runoff | Mar. 31, 2013 Segment, Discontinued Operations GRC Cover OneBeacon Runoff | Mar. 31, 2013 Segment, Discontinued Operations NICO Cover OneBeacon Runoff | May 31, 2001 Segment, Discontinued Operations General Reinsurance Corporation GRC Cover OneBeacon Runoff | Mar. 31, 2013 OneBeacon Runoff Segment, Discontinued Operations | Mar. 31, 2012 OneBeacon Runoff Segment, Discontinued Operations | Feb. 22, 2012 AutoOne Entity | Mar. 31, 2013 OneBeacon Runoff Segment, Discontinued Operations | Mar. 31, 2012 OneBeacon Runoff Segment, Discontinued Operations
Reinsurance [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of insurance companies sold |  |  |  |  |  |  |  |  |  |  |  |  |  | 2 |  |
Loss from sale of discontinued operations |  |  |  | $ 0 | $ 0 |  |  |  |  |  |  |  |  |  |  |
Net income (loss) from discontinued operations, net of tax | 0.5 | (9.3) |  | 0.5 | (9.3) |  |  |  |  |  |  | 0.5 | (9.4) |  |  |
Net favorable and unfavorable loss reserve development | 1.4 | (7.6) |  |  |  |  |  |  |  |  |  |  |  |  | 0.2 | (12.4)
Number of contracts seller caused one beacon to purchase prior to acquisition |  |  |  |  |  |  | 2 |  |  |  |  |  |  |  |  |
Reinsurance recoverable cover under reinsurance contract |  |  |  |  |  |  |  |  | 570.0 | 2,500.0 |  |  |  |  |  |
Adverse loss reserve development on losses occurring in years 2000 and prior |  |  |  |  |  |  |  |  |  |  | 400.0 |  |  |  |  |
Loss reserves ceded at acquisition |  |  |  |  |  |  |  |  |  |  | 170.0 |  |  |  |  |
Reinsurance recoverables |  |  |  |  |  |  | 1,381.0 | 1,401.9 |  |  |  |  |  |  |  |
Reinsurance recoverable on paid losses | 15.6 |  | 17.9 | 14.1 |  | 15.6 | 14.1 |  |  |  |  |  |  |  |  |
Reinsurance recoverables, gross of purchase accounting adjustments |  |  |  |  |  |  | 1,960.9 |  |  |  |  |  |  |  |  |
Purchase accounting adjustments |  |  |  |  |  |  | $ 146.8 |  |  |  |  |  |  |  |  |

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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 310 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6485522&loc=d3e21409-158489 Reference 2: 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 3: 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 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. Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 6 -Article 7 Reference 6: 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 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 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. 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 20 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6480758&loc=d3e6824-158387 Reference 4: 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 + Details
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- Definition Represents the number of reinsurance contracts the seller caused OneBeacon to purchase from subsidiaries of Berkshire Hathaway Inc. immediately prior to the entity's acquisition of OneBeacon. + References No definition available. + Details
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- Definition Reinsurance recoverables gross of purchase accounting adjustments. + References No definition available. + Details
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