Investments (Available For Sale, Fixed Maturity And Equity Security Investments) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Investment [Line Items]
Fixed maturity securities, Amortized Cost	$ 11,731,173	$ 12,011,336
Fixed maturity securities, Unrealized Appreciation	645,088	552,430
Fixed maturity securities, Unrealized Depreciation	(82,737)	(113,297)
Total fixed maturity securities, Market Value	12,293,524	12,450,469
Equity securities, Amortized Cost	463,620	363,283
Equity securities, Unrealized Appreciation	4,060	3,039
Equity securities, Unrealized Depreciation	(18,750)	(2,586)
Equity Securities, Market Value	448,930	363,736
U.S. Treasury Securities And Obligations Of U.S. Government Agencies And Corporations [Member]
Investment [Line Items]
Fixed maturity securities, Amortized Cost	284,514	394,690
Fixed maturity securities, Unrealized Appreciation	16,407	12,772
Fixed maturity securities, Unrealized Depreciation	(287)	(5,655)
Total fixed maturity securities, Market Value	300,634	401,807
Foreign Government Securities [Member]
Investment [Line Items]
Fixed maturity securities, Amortized Cost	1,555,707	1,584,355
Fixed maturity securities, Unrealized Appreciation	120,900	79,661
Fixed maturity securities, Unrealized Depreciation	(8,389)	(25,668)
Total fixed maturity securities, Market Value	1,668,218	1,638,348
Asset-Backed Securities [Member]
Investment [Line Items]
Fixed maturity securities, Amortized Cost	186,936	210,717
Fixed maturity securities, Unrealized Appreciation	7,020	7,799
Fixed maturity securities, Unrealized Depreciation	(550)	(215)
Total fixed maturity securities, Market Value	193,406	218,301
Non-Agency Residential Mortgage-Backed Securities [Member]
Investment [Line Items]
Fixed maturity securities, Amortized Cost	53,365	76,259
Fixed maturity securities, Unrealized Appreciation	499	1,205
Fixed maturity securities, Unrealized Depreciation	(775)	(1,723)
Total fixed maturity securities, Market Value	53,089	75,741
Agency Residential Mortgage-Backed Securities [Member]
Investment [Line Items]
Fixed maturity securities, Amortized Cost	2,198,937	2,018,384
Fixed maturity securities, Unrealized Appreciation	86,722	76,367
Fixed maturity securities, Unrealized Depreciation	(3,066)	(1,469)
Total fixed maturity securities, Market Value	2,282,593	2,093,282
Commercial Mortgage-Backed Securities [Member]
Investment [Line Items]
Fixed maturity securities, Amortized Cost	310,387	324,922
Fixed maturity securities, Unrealized Appreciation	20,942	17,751
Fixed maturity securities, Unrealized Depreciation	(9,902)	(5,454)
Total fixed maturity securities, Market Value	321,427	337,219
Foreign Corporate Securities [Member]
Investment [Line Items]
Fixed maturity securities, Amortized Cost	2,086,951	1,675,518
Fixed maturity securities, Unrealized Appreciation	91,869	71,268
Fixed maturity securities, Unrealized Depreciation	(32,189)	(31,666)
Total fixed maturity securities, Market Value	2,146,631	1,715,120
Obligations Of U.S. States And Political Subdivisions [Member]
Investment [Line Items]
Fixed maturity securities, Amortized Cost	1,558,615	2,809,514
Fixed maturity securities, Unrealized Appreciation	102,815	116,920
Fixed maturity securities, Unrealized Depreciation	(525)	(24,929)
Total fixed maturity securities, Market Value	1,660,905	2,901,505
Corporate Securities [Member]
Investment [Line Items]
Fixed maturity securities, Amortized Cost	3,495,761	2,916,977
Fixed maturity securities, Unrealized Appreciation	197,914	168,687
Fixed maturity securities, Unrealized Depreciation	(27,054)	(16,518)
Total fixed maturity securities, Market Value	$ 3,666,621	$ 3,069,146

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For an unclassified balance sheet, total of equity securities at market value. Unrealized gains and losses of such securities are excluded from earnings and included in other comprehensive income, a separate component of shareholders' equity.

+ References

No definition available.

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- Definition

Available For Sale Securities Equity, Unrealized Appreciation

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Available For Sale Securities Equity, Unrealized Depreciation

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- Definition

For an unclassified balance sheet, total of fixed maturity securities at market value categorized neither as held-to-maturity nor trading. Unrealized gains and losses of such securities are excluded from earnings and included in other comprehensive income, a separate component of shareholders' equity.

+ References

No definition available.

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This item represents the cost of equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments for other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

No definition available.

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This item represents the total of all debt securities grouped by maturity dates, at cost, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments, as defined), and fair value hedge accounting adjustments, if any, which are classified neither as held-to-maturity nor trading securities.

+ References

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

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS115-1/124-1

-Paragraph 7

-Footnote 2

-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 20

-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 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.2)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

This item represents the gross unrealized gains for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 22

-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 13, 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

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6872113&loc=d3e27161-111563

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- Definition

This item represents the gross unrealized losses for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.

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No definition available.

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