Fair Value Measurement (Schedule Of Assets And Liabilities Measured At Fair Value On A Recurring Basis Valuation Techniques) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Fair Value Measurement [Line Items]
Assets	$ 3,160,613	$ 3,062,421
Liabilities	431	1,325
Level 1 [Member]
Fair Value Measurement [Line Items]
Assets	649,127	600,692
Liabilities	171	655
Level 2 [Member]
Fair Value Measurement [Line Items]
Assets	2,419,554	2,404,218
Liabilities	260	670
Level 3 [Member]
Fair Value Measurement [Line Items]
Assets	91,932	57,511
Liabilities	0	0
Short-term bonds [Member]
Fair Value Measurement [Line Items]
Assets	32,695	9,011
Short-term bonds [Member] | Level 1 [Member]
Fair Value Measurement [Line Items]
Assets	0	0
Short-term bonds [Member] | Level 2 [Member]
Fair Value Measurement [Line Items]
Assets	32,695	9,011
Short-term bonds [Member] | Level 3 [Member]
Fair Value Measurement [Line Items]
Assets	0	0
Money market instruments [Member]
Fair Value Measurement [Line Items]
Assets	188,387	227,433
Money market instruments [Member] | Level 1 [Member]
Fair Value Measurement [Line Items]
Assets	188,387	227,433
Money market instruments [Member] | Level 2 [Member]
Fair Value Measurement [Line Items]
Assets	0	0
Money market instruments [Member] | Level 3 [Member]
Fair Value Measurement [Line Items]
Assets	0	0
Equity contracts [Member]
Fair Value Measurement [Line Items]
Assets	1
Liabilities	171	655
Equity contracts [Member] | Level 1 [Member]
Fair Value Measurement [Line Items]
Assets	1
Liabilities	171	655
Equity contracts [Member] | Level 2 [Member]
Fair Value Measurement [Line Items]
Assets	0
Liabilities	0	0
Equity contracts [Member] | Level 3 [Member]
Fair Value Measurement [Line Items]
Assets	0
Liabilities	0	0
Interest rate swap agreements [Member]
Fair Value Measurement [Line Items]
Liabilities	260	670
Interest rate swap agreements [Member] | Level 1 [Member]
Fair Value Measurement [Line Items]
Liabilities	0	0
Interest rate swap agreements [Member] | Level 2 [Member]
Fair Value Measurement [Line Items]
Liabilities	260	670
Interest rate swap agreements [Member] | Level 3 [Member]
Fair Value Measurement [Line Items]
Liabilities	0	0
Fixed maturity securities [Member] | U.S. government bonds and agencies [Member]
Fair Value Measurement [Line Items]
Assets	12,153	14,298
Fixed maturity securities [Member] | U.S. government bonds and agencies [Member] | Level 1 [Member]
Fair Value Measurement [Line Items]
Assets	12,153	14,298
Fixed maturity securities [Member] | U.S. government bonds and agencies [Member] | Level 2 [Member]
Fair Value Measurement [Line Items]
Assets	0	0
Fixed maturity securities [Member] | U.S. government bonds and agencies [Member] | Level 3 [Member]
Fair Value Measurement [Line Items]
Assets	0	0
Fixed maturity securities [Member] | Municipal securities [Member]
Fair Value Measurement [Line Items]
Assets	2,205,136	2,271,275
Fixed maturity securities [Member] | Municipal securities [Member] | Level 1 [Member]
Fair Value Measurement [Line Items]
Assets	0	0
Fixed maturity securities [Member] | Municipal securities [Member] | Level 2 [Member]
Fair Value Measurement [Line Items]
Assets	2,205,136	2,271,275
Fixed maturity securities [Member] | Municipal securities [Member] | Level 3 [Member]
Fair Value Measurement [Line Items]
Assets	0	0
Fixed maturity securities [Member] | Mortgage-backed securities [Member]
Fair Value Measurement [Line Items]
Assets	32,418	37,371
Fixed maturity securities [Member] | Mortgage-backed securities [Member] | Level 1 [Member]
Fair Value Measurement [Line Items]
Assets	0	0
Fixed maturity securities [Member] | Mortgage-backed securities [Member] | Level 2 [Member]
Fair Value Measurement [Line Items]
Assets	32,418	37,371
Fixed maturity securities [Member] | Mortgage-backed securities [Member] | Level 3 [Member]
Fair Value Measurement [Line Items]
Assets	0	0
Fixed maturity securities [Member] | Corporate securities [Member]
Fair Value Measurement [Line Items]
Assets	137,653	75,142
Fixed maturity securities [Member] | Corporate securities [Member] | Level 1 [Member]
Fair Value Measurement [Line Items]
Assets	0	0
Fixed maturity securities [Member] | Corporate securities [Member] | Level 2 [Member]
Fair Value Measurement [Line Items]
Assets	137,653	75,142
Fixed maturity securities [Member] | Corporate securities [Member] | Level 3 [Member]
Fair Value Measurement [Line Items]
Assets	0	0
Fixed maturity securities [Member] | Collateralized debt obligations [Member]
Fair Value Measurement [Line Items]
Assets	81,357	47,503
Fixed maturity securities [Member] | Collateralized debt obligations [Member] | Level 1 [Member]
Fair Value Measurement [Line Items]
Assets	0	0
Fixed maturity securities [Member] | Collateralized debt obligations [Member] | Level 2 [Member]
Fair Value Measurement [Line Items]
Assets	0	0
Fixed maturity securities [Member] | Collateralized debt obligations [Member] | Level 3 [Member]
Fair Value Measurement [Line Items]
Assets	81,357	47,503
Equity securities [Member] | Public utilities [Member]
Fair Value Measurement [Line Items]
Assets	83,187	26,342
Equity securities [Member] | Public utilities [Member] | Level 1 [Member]
Fair Value Measurement [Line Items]
Assets	83,187	26,342
Equity securities [Member] | Public utilities [Member] | Level 2 [Member]
Fair Value Measurement [Line Items]
Assets	0	0
Equity securities [Member] | Public utilities [Member] | Level 3 [Member]
Fair Value Measurement [Line Items]
Assets	0	0
Equity securities [Member] | Banks, trusts and insurance companies [Member]
Fair Value Measurement [Line Items]
Assets	18,546	16,027
Equity securities [Member] | Banks, trusts and insurance companies [Member] | Level 1 [Member]
Fair Value Measurement [Line Items]
Assets	18,546	16,027
Equity securities [Member] | Banks, trusts and insurance companies [Member] | Level 2 [Member]
Fair Value Measurement [Line Items]
Assets	0	0
Equity securities [Member] | Banks, trusts and insurance companies [Member] | Level 3 [Member]
Fair Value Measurement [Line Items]
Assets	0	0
Equity securities [Member] | Energy and other [Member]
Fair Value Measurement [Line Items]
Assets	346,853	316,592
Equity securities [Member] | Energy and other [Member] | Level 1 [Member]
Fair Value Measurement [Line Items]
Assets	346,853	316,592
Equity securities [Member] | Energy and other [Member] | Level 2 [Member]
Fair Value Measurement [Line Items]
Assets	0	0
Equity securities [Member] | Energy and other [Member] | Level 3 [Member]
Fair Value Measurement [Line Items]
Assets	0	0
Equity securities [Member] | Non-redeemable preferred stock [Member]
Fair Value Measurement [Line Items]
Assets	11,652	11,419
Equity securities [Member] | Non-redeemable preferred stock [Member] | Level 1 [Member]
Fair Value Measurement [Line Items]
Assets	0	0
Equity securities [Member] | Non-redeemable preferred stock [Member] | Level 2 [Member]
Fair Value Measurement [Line Items]
Assets	11,652	11,419
Equity securities [Member] | Non-redeemable preferred stock [Member] | Level 3 [Member]
Fair Value Measurement [Line Items]
Assets	0	0
Equity securities [Member] | Partnership interest in a private credit fund [Member]
Fair Value Measurement [Line Items]
Assets	10,575	10,008
Equity securities [Member] | Partnership interest in a private credit fund [Member] | Level 1 [Member]
Fair Value Measurement [Line Items]
Assets	0	0
Equity securities [Member] | Partnership interest in a private credit fund [Member] | Level 2 [Member]
Fair Value Measurement [Line Items]
Assets	0	0
Equity securities [Member] | Partnership interest in a private credit fund [Member] | Level 3 [Member]
Fair Value Measurement [Line Items]
Assets	$ 10,575	$ 10,008