Fair Value (Fair Value Measurement Levels For All Assets And Liabilities) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total fixed maturities, market value	$ 12,293,524	$ 12,450,469
Fixed maturities, fair value	113,606	180,482
Equity securities, market value	448,930	363,736
Equity securities, fair value	1,249,106	721,449
Equity index put option contracts	69,729	58,467
U.S. Government Agencies And Corporations [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total fixed maturities, market value	300,634	401,807
Obligations Of U.S. States And Political Subdivisions [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total fixed maturities, market value	1,660,905	2,901,505
Corporate Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total fixed maturities, market value	3,666,621	3,069,146
Asset-Backed Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total fixed maturities, market value	193,406	218,301
Commercial Mortgage-Backed Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total fixed maturities, market value	321,427	337,219
Agency Residential Mortgage-Backed Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total fixed maturities, market value	2,282,593	2,093,282
Non-Agency Residential Mortgage-Backed Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total fixed maturities, market value	53,089	75,741
Foreign Government Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total fixed maturities, market value	1,668,218	1,638,348
Foreign Corporate Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total fixed maturities, market value	2,146,631	1,715,120
Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity securities, market value	433,278	363,736
Equity securities, fair value	1,133,011	721,449
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total fixed maturities, market value	12,273,057	12,443,558
Fixed maturities, fair value	113,606	180,482
Equity securities, market value	15,652
Equity securities, fair value	116,095
Significant Other Observable Inputs (Level 2) [Member] \| U.S. Government Agencies And Corporations [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total fixed maturities, market value	300,634	401,807
Significant Other Observable Inputs (Level 2) [Member] \| Obligations Of U.S. States And Political Subdivisions [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total fixed maturities, market value	1,660,905	2,901,505
Significant Other Observable Inputs (Level 2) [Member] \| Corporate Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total fixed maturities, market value	3,666,621	3,069,146
Significant Other Observable Inputs (Level 2) [Member] \| Asset-Backed Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total fixed maturities, market value	176,469	217,306
Significant Other Observable Inputs (Level 2) [Member] \| Commercial Mortgage-Backed Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total fixed maturities, market value	321,427	337,219
Significant Other Observable Inputs (Level 2) [Member] \| Agency Residential Mortgage-Backed Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total fixed maturities, market value	2,282,593	2,093,282
Significant Other Observable Inputs (Level 2) [Member] \| Non-Agency Residential Mortgage-Backed Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total fixed maturities, market value	52,603	74,241
Significant Other Observable Inputs (Level 2) [Member] \| Foreign Government Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total fixed maturities, market value	1,668,218	1,638,348
Significant Other Observable Inputs (Level 2) [Member] \| Foreign Corporate Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total fixed maturities, market value	2,143,587	1,710,704
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total fixed maturities, market value	20,467	6,911
Equity index put option contracts	69,729	58,467
Significant Unobservable Inputs (Level 3) [Member] \| Asset-Backed Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total fixed maturities, market value	16,937	995
Significant Unobservable Inputs (Level 3) [Member] \| Non-Agency Residential Mortgage-Backed Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total fixed maturities, market value	486	1,500
Significant Unobservable Inputs (Level 3) [Member] \| Foreign Corporate Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total fixed maturities, market value	$ 3,044	$ 4,416

For an unclassified balance sheet, total of debt securities categorized neither as held-to-maturity nor trading.

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

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Reference 9: http://www.xbrl.org/2003/role/presentationRef

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+ Details

- Definition

For an unclassified balance sheet, this item represents equity securities categorized neither as held-to-maturity nor trading.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 3

-Subparagraph c

-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 FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 19

-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 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

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-Publisher FASB

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-Publisher FASB

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Reference 10: http://www.xbrl.org/2003/role/presentationRef

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+ Details