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Fair Value Measurements (Schedule Of Assets And Liabilities Measured At Fair Value On A Recurring Basis Valuation Techniques) (Details) (USD $) In Thousands, unless otherwise specified | Dec. 31, 2011 | Dec. 31, 2010
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Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | $ 3,062,421 | $ 3,159,497
Total liabilities at fair value | 1,325 | 5,818
Level 1 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | 600,692 | 484,971
Total liabilities at fair value | 655 | 2,776
Level 2 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | 2,404,218 | 2,617,210
Total liabilities at fair value | 670 | 3,042
Level 3 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | 57,511 | 57,316
Total liabilities at fair value | 0 | 0
Short-Term Bonds [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | 9,011 | 17,043
Short-Term Bonds [Member] | Level 1 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | 0 | 0
Short-Term Bonds [Member] | Level 2 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | 9,011 | 17,043
Short-Term Bonds [Member] | Level 3 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | 0 | 0
Money Market Instruments [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | 227,433 | 126,328
Money Market Instruments [Member] | Level 1 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | 227,433 | 126,328
Money Market Instruments [Member] | Level 2 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | 0 | 0
Money Market Instruments [Member] | Level 3 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | 0 | 0
Equity Contracts [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total liabilities at fair value | 655 | 2,776
Equity Contracts [Member] | Level 1 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total liabilities at fair value | 655 | 2,776
Equity Contracts [Member] | Level 2 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total liabilities at fair value | 0 | 0
Equity Contracts [Member] | Level 3 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total liabilities at fair value | 0 | 0
Interest Rate Swaps Agreements [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value |  | 4,240
Total liabilities at fair value | 670 | 3,042
Interest Rate Swaps Agreements [Member] | Level 1 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value |  | 0
Total liabilities at fair value | 0 | 0
Interest Rate Swaps Agreements [Member] | Level 2 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value |  | 4,240
Total liabilities at fair value | 670 | 3,042
Interest Rate Swaps Agreements [Member] | Level 3 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value |  | 0
Total liabilities at fair value | 0 | 0
Fixed Maturity Securities [Member] | U.S. Government Bonds And Agencies [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | 14,298 | 8,805
Fixed Maturity Securities [Member] | U.S. Government Bonds And Agencies [Member] | Level 1 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | 14,298 | 8,805
Fixed Maturity Securities [Member] | U.S. Government Bonds And Agencies [Member] | Level 2 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | 0 | 0
Fixed Maturity Securities [Member] | U.S. Government Bonds And Agencies [Member] | Level 3 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | 0 | 0
Fixed Maturity Securities [Member] | Municipal Securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | 2,271,275 | 2,435,213
Fixed Maturity Securities [Member] | Municipal Securities [Member] | Level 1 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | 0 | 0
Fixed Maturity Securities [Member] | Municipal Securities [Member] | Level 2 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | 2,271,275 | 2,433,589
Fixed Maturity Securities [Member] | Municipal Securities [Member] | Level 3 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | 0 | 1,624
Fixed Maturity Securities [Member] | Mortgage-Backed Securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | 37,371 | 57,367
Fixed Maturity Securities [Member] | Mortgage-Backed Securities [Member] | Level 1 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | 0 | 0
Fixed Maturity Securities [Member] | Mortgage-Backed Securities [Member] | Level 2 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | 37,371 | 57,367
Fixed Maturity Securities [Member] | Mortgage-Backed Securities [Member] | Level 3 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | 0 | 0
Fixed Maturity Securities [Member] | Corporate Securities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | 75,142 | 95,203
Fixed Maturity Securities [Member] | Corporate Securities [Member] | Level 1 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | 0 | 0
Fixed Maturity Securities [Member] | Corporate Securities [Member] | Level 2 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | 75,142 | 95,203
Fixed Maturity Securities [Member] | Corporate Securities [Member] | Level 3 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | 0 | 0
Fixed Maturity Securities [Member] | Collateralized Debt Obligations [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | 47,503 | 55,692
Fixed Maturity Securities [Member] | Collateralized Debt Obligations [Member] | Level 1 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | 0 | 0
Fixed Maturity Securities [Member] | Collateralized Debt Obligations [Member] | Level 2 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | 0 | 0
Fixed Maturity Securities [Member] | Collateralized Debt Obligations [Member] | Level 3 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | 47,503 | 55,692
Equity Securities [Member] | Public Utilities [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | 26,342 | 27,214
Equity Securities [Member] | Public Utilities [Member] | Level 1 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | 26,342 | 27,214
Equity Securities [Member] | Public Utilities [Member] | Level 2 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | 0 | 0
Equity Securities [Member] | Public Utilities [Member] | Level 3 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | 0 | 0
Equity Securities [Member] | Banks, Trusts And Insurance Companies [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | 16,027 | 20,521
Equity Securities [Member] | Banks, Trusts And Insurance Companies [Member] | Level 1 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | 16,027 | 20,521
Equity Securities [Member] | Banks, Trusts And Insurance Companies [Member] | Level 2 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | 0 | 0
Equity Securities [Member] | Banks, Trusts And Insurance Companies [Member] | Level 3 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | 0 | 0
Equity Securities [Member] | Industrial And Other [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | 316,592 | 302,103
Equity Securities [Member] | Industrial And Other [Member] | Level 1 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | 316,592 | 302,103
Equity Securities [Member] | Industrial And Other [Member] | Level 2 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | 0 | 0
Equity Securities [Member] | Industrial And Other [Member] | Level 3 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | 0 | 0
Equity Securities [Member] | Non-Redeemable Preferred Stock [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | 11,419 | 9,768
Equity Securities [Member] | Non-Redeemable Preferred Stock [Member] | Level 1 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | 0 | 0
Equity Securities [Member] | Non-Redeemable Preferred Stock [Member] | Level 2 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | 11,419 | 9,768
Equity Securities [Member] | Non-Redeemable Preferred Stock [Member] | Level 3 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | 0 | 0
Equity Securities [Member] | Partnership Interest In A Private Credit Fund [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | 10,008 |
Equity Securities [Member] | Partnership Interest In A Private Credit Fund [Member] | Level 1 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | 0 |
Equity Securities [Member] | Partnership Interest In A Private Credit Fund [Member] | Level 2 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | 0 |
Equity Securities [Member] | Partnership Interest In A Private Credit Fund [Member] | Level 3 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets at fair value | $ 10,008 |

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