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Segment Information (Revenue From Continuing Operations by Segment) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Total net premiums earned	$ 373,427	$ 358,963	$ 355,580	$ 351,343	$ 353,497	$ 354,709	$ 352,190	$ 356,202	$ 1,439,313	$ 1,416,598	$ 1,431,047
Other income									8,479	9,398	10,470
Total Insurance Operations revenues									1,447,382	1,425,828	1,441,487
Net investment income	28,839	35,786	39,345	43,473	41,471	32,986	36,545	34,706	147,443	145,708	118,471
Net realized gain on investments									2,240	(7,083)	(45,970)
Total investment income, before federal income tax									149,683	138,625	72,501
Total all segments									1,597,065	1,564,453	1,513,988
Total revenues									1,597,475	1,564,621	1,514,018
Commercial Automobile [Member]
Total net premiums earned									279,610	291,495	300,562
Workers Compensation [Member]
Total net premiums earned									259,354	252,441	263,490
General Liability [Member]
Total net premiums earned									344,682	336,475	362,479
Commercial Property [Member]
Total net premiums earned									192,989	199,252	197,665
Business Owners Policies [Member]
Total net premiums earned									66,225	65,260	62,638
Bonds Segment [Member]
Total net premiums earned									18,910	19,243	18,455
Other Commercial [Member]
Total net premiums earned									13,091	10,116	9,663
Total Commercial Lines [Member]
Total net premiums earned									1,174,861	1,174,282	1,214,952
Personal Automobile [Member]
Total net premiums earned									148,824	141,962	133,320
Homeowners [Member]
Total net premiums earned									102,764	87,862	73,076
Other Personal [Member]
Total net premiums earned									12,864	12,492	9,699
Total Personal Lines [Member]
Total net premiums earned									264,452	242,316	216,095
Miscellaneous Income [Member]
Other income									8,069	9,230	10,440
Other Income [Member]
Other income									$ 410	$ 168	$ 30

X

- Definition

The income earned from investments in securities and other investments including dividends, interest, and returns on other investments. This item does not include realized gains (losses).

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The income earned from investments in securities and other investments including dividends, interest, and returns on other investments, including realized gains/losses.

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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)

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Reflects the sum of all other revenue and income recognized by the entity in the period not otherwise specified in the income statement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 7

-Section 04

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Premiums recognized as revenue in the period earned on all property and casualty insurance and reinsurance contracts after subtracting any amounts ceded to another insurer.

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-Publisher FASB

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-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.



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The net realized gains or losses on investments during the period, not including gains or losses on securities separately or otherwise categorized as trading, available-for-sale, or held-to-maturity.

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Aggregate revenue recognized during the period (derived from goods sold, services rendered, insurance premiums, or other activities that constitute an entity's earning process). For financial services companies, also includes investment and interest income, and sales and trading gains.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

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-Article 5

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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.

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