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Reinsurance (List of Direct, Assumed, and Ceded Reinsurance Amounts) (Details) (USD $) | 3 Months Ended |
--- | --- | ---
Mar. 31, 2013 | Mar. 31, 2012 | Mar. 31, 2013 Hurricane Sandy [Member] | Dec. 31, 2012 Hurricane Sandy [Member]
Premiums written: |  |  |  |
Direct | $ 528,816,000 | $ 475,966,000 |  |
Assumed | 8,482,000 | 21,989,000 |  |
Ceded premiums written | (87,174,000) | (77,783,000) |  |
Net | 450,124,000 | 420,172,000 |  |
Premiums earned: |  |  |  |
Direct | 494,066,000 | 451,988,000 |  |
Assumed | 12,463,000 | 15,049,000 |  |
Ceded premiums earned | (85,589,000) | (88,208,000) |  |
Net | 420,940,000 | 378,829,000 |  |
Loss and loss expense incurred: |  |  |  |
Direct | 365,646,000 | 252,203,000 | 55,000,000 |
Assumed | 9,074,000 | 10,599,000 |  |
Ceded loss and loss expense incurred | (104,871,000) | (9,896,000) |  |
Net | 269,849,000 | 252,906,000 |  |
Number of insurance subsidiaries | 10 |  |  |
Estimated flood gross losses |  |  | $ 1,094,000,000 | $ 1,039,000,000
Percentage of unpaid NFIP claims ceded by federal government | 100.00% |  |  |

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- Definition Premiums assumed and earned for all property and casualty insurance assumed from other insurers as a result of reinsurance arrangements. + 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 (b),(c)(2)-(3) -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 17 -Article 12 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 113 -Paragraph 27 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 235 -Section S99 -Paragraph 2 -Subparagraph (SX 210.12-17) -URI http://asc.fasb.org/extlink&oid=6588446&loc=d3e574992-122915 + Details
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