Property and Liability Insurance Earned Premiums (Schedule of Property and Liability Insurance Earned Premiums) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Supplementary Insurance Information [Abstract]
Direct amounts	$ 2,578,715	$ 2,569,661	$ 2,569,942
Ceded to other companies	(5,066)	(4,134)	(4,468)
Assumed	1,271	530	1,211
Net amounts	$ 2,574,920	$ 2,566,057	$ 2,566,685

Premiums assumed for all property and casualty insurance assumed from other insurers as a result of reinsurance arrangements.

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 17

-Article 12

Reference 2: 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)

-URI http://asc.fasb.org/extlink&oid=6486672&loc=d3e27261-158547

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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.

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Premiums for property and casualty coverage ceded to another insurer under reinsurance arrangements.

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Amount of net investment income earned by property-casualty insurance underwriter.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 235

-Section S99

-Paragraph 3

-Subparagraph (SX 210.12-18)

-URI http://asc.fasb.org/extlink&oid=6588446&loc=d3e575016-122915

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 18

-Article 12

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Amount of actual premium written by property-casualty insurance underwriter.

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