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Segment Information (Revenue From Continuing Operations by Segment) (Details) (USD $) In Thousands, unless otherwise specified | 3 Months Ended
--- | ---
Mar. 31, 2014 | Mar. 31, 2013
Segment Reporting Information [Line Items] |  |
Total net premiums earned | $ 456,495 | $ 420,940
Other income | 9,824 | 2,784
Net investment income | 35,534 | 32,870
Net realized investment gains | 7,218 | 3,355
Total investment revenues | 42,752 | 36,225
Total all segments | 509,066 | 459,885
Total revenues | 509,071 | 459,949
Commercial Automobile [Member] |  |
Segment Reporting Information [Line Items] |  |
Total net premiums earned | 82,216 | 74,347
Workers Compensation [Member] |  |
Segment Reporting Information [Line Items] |  |
Total net premiums earned | 69,413 | 66,084
General Liability [Member] |  |
Segment Reporting Information [Line Items] |  |
Total net premiums earned | 108,818 | 97,703
Commercial Property [Member] |  |
Segment Reporting Information [Line Items] |  |
Total net premiums earned | 60,186 | 53,415
Business Owners' Policies [Member] |  |
Segment Reporting Information [Line Items] |  |
Total net premiums earned | 20,869 | 18,540
Bonds Segment [Member] |  |
Segment Reporting Information [Line Items] |  |
Total net premiums earned | 4,756 | 4,764
Other Commercial [Member] |  |
Segment Reporting Information [Line Items] |  |
Total net premiums earned | 3,183 | 2,992
Total Standard Commercial Lines [Member] |  |
Segment Reporting Information [Line Items] |  |
Total net premiums earned | 349,441 | 317,845
Personal Automobile [Member] |  |
Segment Reporting Information [Line Items] |  |
Total net premiums earned | 38,226 | 38,393
Homeowners [Member] |  |
Segment Reporting Information [Line Items] |  |
Total net premiums earned | 33,298 | 31,135
Other Personal [Member] |  |
Segment Reporting Information [Line Items] |  |
Total net premiums earned | 3,294 | 3,508
Total standard Personal Lines [Member] |  |
Segment Reporting Information [Line Items] |  |
Total net premiums earned | 74,818 | 73,036
Total Standard Insurance Operations [Member] |  |
Segment Reporting Information [Line Items] |  |
Total net premiums earned | 424,259 | 390,881
Total insurance operations revenues | 434,078 | 393,601
Miscellaneous Income [Member] |  |
Segment Reporting Information [Line Items] |  |
Other income | 9,819 | 2,720
Excess And Surplus Operations [Member] |  |
Segment Reporting Information [Line Items] |  |
Total net premiums earned | 32,236 | 30,059
Other Income [Member] |  |
Segment Reporting Information [Line Items] |  |
Other income | $ 5 | $ 64

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- Definition Amount of total revenue for the reportable segments, including revenue from external customers, transactions with other operating segments of the same entity, and (gross) interest revenue. All considered to be "operating revenue" for purposes of the taxonomy. + References No definition available. + Details
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- Definition Revenue from insurance services, including net premiums earned, gain on sale of insurance block, agency management fees and insurance contract fees and commissions. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04.1,4) -URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913 + Details
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- Definition Amount, after premiums ceded to other entities and premiums assumed by the entity, of property and casualty premiums earned. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04.1) -URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph 1 -Article 7 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 605 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6486662&loc=d3e27175-158546 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 605 -Section 50 -Paragraph 1 -Subparagraph (b),(c) -URI http://asc.fasb.org/extlink&oid=6486672&loc=d3e27261-158547 + Details
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