Investments (Summary Of Unrealized Appreciation (Depreciation) Of Available For Sale, Fixed Maturity And Equity Security Investments) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Fixed Maturity Securities [Member]
Investment [Line Items]
Amortized Cost	$ 5,289,619	$ 4,880,654
Unrealized Appreciation	262,094	261,842
Unrealized Depreciation	(20,303)	(35,468)
Market Value	5,531,410	5,107,028
U.S. Treasury Securities And Obligations Of U.S. Government Agencies And Corporations [Member]
Investment [Line Items]
Amortized Cost	77,611	77,351
Unrealized Appreciation	1,448	2,475
Unrealized Depreciation	(869)	(287)
Market Value	78,190	79,539
States, Municipalities And Political Subdivisions [Member]
Investment [Line Items]
Amortized Cost	1,214,990	1,558,615
Unrealized Appreciation	78,096	102,815
Unrealized Depreciation	(1,123)	(525)
Market Value	1,291,963	1,660,905
Corporate Debt Securities [Member]
Investment [Line Items]
Amortized Cost	1,510,186	1,200,941
Unrealized Appreciation	61,137	45,070
Unrealized Depreciation	(6,471)	(17,776)
Market Value	1,564,852	1,228,235
Asset-backed Securities [Member]
Investment [Line Items]
Amortized Cost	44,070	44,351
Unrealized Appreciation	2,417	758
Unrealized Depreciation		(6)
Market Value	46,487	45,103
Mortgage-Backed Securities Commercial [Member]
Investment [Line Items]
Amortized Cost	45,157	41,953
Unrealized Appreciation	7,534	7,187
Unrealized Depreciation	(67)	(1,266)
Market Value	52,624	47,874
Agency Residential [Member]
Investment [Line Items]
Amortized Cost	672,724	528,946
Unrealized Appreciation	12,722	16,209
Unrealized Depreciation	(1,724)	(1,762)
Market Value	683,722	543,393
Non-agency Residential [Member]
Investment [Line Items]
Amortized Cost	1,933	24,139
Unrealized Appreciation	429	470
Unrealized Depreciation	(33)	(320)
Market Value	2,329	24,289
Foreign Government Securities [Member]
Investment [Line Items]
Amortized Cost	732,277	733,814
Unrealized Appreciation	51,461	57,437
Unrealized Depreciation	(3,735)	(2,602)
Market Value	780,003	788,649
Foreign Corporate Securities [Member]
Investment [Line Items]
Amortized Cost	990,671	670,544
Unrealized Appreciation	46,850	29,421
Unrealized Depreciation	(6,281)	(10,924)
Market Value	1,031,240	689,041
Equity Securities [Member]
Investment [Line Items]
Amortized Cost	15	15
Unrealized Depreciation	(2)	(5)
Market Value	$ 13	$ 10

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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

-Publisher FASB

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 12

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

-Publisher FASB

-Name Accounting Standards Codification

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Reference 4: http://www.xbrl.org/2003/role/presentationRef

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-Number 115

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Reference 5: http://www.xbrl.org/2003/role/presentationRef

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-Number FAS115-1/124-1

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Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 13

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 14

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

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+ Details

- Definition

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

+ References+ Details

- 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+ Details