Investments (Details 2) (USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended
Jun. 30, 2012	Dec. 31, 2011
Fixed Maturities and Equity Securities
Amortized Cost/Cost	$ 5,146,873	$ 4,984,389
Unrealized Gains	564,090	470,496
Unrealized Losses	16,237	33,053
Fair value of issued securities	5,694,726	5,421,832
OTTI in AOCI	2,435	2,136
Equity securities Amortized Cost/Cost	37,199	23,070
Equity securities Fair Value	38,035	26,774
Mortgage-backed securities [Member]
Fixed Maturities and Equity Securities
Amortized Cost/Cost	552,090	532,554
Unrealized Gains	77,445	71,402
Unrealized Losses	5	144
Fair value of issued securities	629,530	603,812
Other [Member]
Fixed Maturities and Equity Securities
Amortized Cost/Cost	451,983	560,036
Unrealized Gains	37,070	43,705
Unrealized Losses	103
Fair value of issued securities	488,950	603,741
Municipal bonds [Member]
Fixed Maturities and Equity Securities
Amortized Cost/Cost	1,349,819	1,291,281
Unrealized Gains	162,108	122,857
Unrealized Losses	2,419	1,020
Fair value of issued securities	1,509,508	1,413,118
Foreign government bonds [Member]
Fixed Maturities and Equity Securities
Amortized Cost/Cost	48,503	44,529
Unrealized Gains	7,103	5,095
Fair value of issued securities	55,606	49,624
Corporate bonds [Member]
Fixed Maturities and Equity Securities
Amortized Cost/Cost	2,174,764	1,967,229
Unrealized Gains	250,421	205,413
Unrealized Losses	10,720	16,098
Fair value of issued securities	2,414,465	2,156,544
Other mortgage-backed securities [Member]
Fixed Maturities and Equity Securities
Amortized Cost/Cost	569,714	588,760
Unrealized Gains	29,943	22,024
Unrealized Losses	2,990	15,791
Fair value of issued securities	596,667	594,993
OTTI in AOCI	2,435	2,136
Equity Securities [Member]
Fixed Maturities and Equity Securities
Unrealized Gains	2,013	4,030
Unrealized Losses	$ 1,177	$ 326

Amount of debt securities categorized neither as held-to-maturity nor trading.

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+ Details

- Definition

Amount of equity securities categorized neither as held-to-maturity nor as trading.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

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-Publisher FASB

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-Publisher FASB

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

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

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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.

+ 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

- Definition

Before tax amount of other than temporary impairment (OTTI) on a debt security, categorized as either available-for-sale or held-to-maturity, recognized in other comprehensive income (loss).

+ References

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+ Details