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	Mar. 31, 2013	Dec. 31, 2012
Fair Value Measurement [Line Items]
Assets	$ 3,204,757	$ 3,180,095
Liabilities	628	278
Level 1 [Member]
Fair Value Measurement [Line Items]
Assets	645,114	738,408
Liabilities	628	175
Level 2 [Member]
Fair Value Measurement [Line Items]
Assets	2,508,328	2,387,580
Liabilities	0	103
Level 3 [Member]
Fair Value Measurement [Line Items]
Assets	51,315	54,107
Liabilities	0	0
Short-term bonds [Member]
Fair Value Measurement [Line Items]
Assets	39,128	24,530
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	39,128	24,530
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	112,953	270,123
Money market instruments [Member] | Level 1 [Member]
Fair Value Measurement [Line Items]
Assets	112,953	270,123
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]
Liabilities	628	175
Equity contracts [Member] | Level 1 [Member]
Fair Value Measurement [Line Items]
Liabilities	628	175
Equity contracts [Member] | Level 2 [Member]
Fair Value Measurement [Line Items]
Liabilities	0	0
Equity contracts [Member] | Level 3 [Member]
Fair Value Measurement [Line Items]
Liabilities	0	0
Interest Rate Swap Agreements [Member]
Fair Value Measurement [Line Items]
Liabilities		103
Interest Rate Swap Agreements [Member] | Level 1 [Member]
Fair Value Measurement [Line Items]
Liabilities		0
Interest Rate Swap Agreements [Member] | Level 2 [Member]
Fair Value Measurement [Line Items]
Liabilities		103
Interest Rate Swap Agreements [Member] | Level 3 [Member]
Fair Value Measurement [Line Items]
Liabilities		0
Fixed maturity securities [Member] | U.S. government bonds and agencies [Member]
Fair Value Measurement [Line Items]
Assets	16,375	14,204
Fixed maturity securities [Member] | U.S. government bonds and agencies [Member] | Level 1 [Member]
Fair Value Measurement [Line Items]
Assets	16,375	14,204
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	2,192,651	2,165,095
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	2,192,651	2,165,095
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	31,177	30,703
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	31,177	30,703
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	233,492	155,551
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	233,492	155,551
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	39,723	42,801
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	39,723	42,801
Equity securities [Member] | Public utilities [Member]
Fair Value Measurement [Line Items]
Assets	104,715	85,106
Equity securities [Member] | Public utilities [Member] | Level 1 [Member]
Fair Value Measurement [Line Items]
Assets	104,715	85,106
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	24,461	22,166
Equity securities [Member] | Banks, trusts and insurance companies [Member] | Level 1 [Member]
Fair Value Measurement [Line Items]
Assets	24,461	22,166
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	386,610	346,809
Equity securities [Member] | Energy and other [Member] | Level 1 [Member]
Fair Value Measurement [Line Items]
Assets	386,610	346,809
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
Fair Value Measurement [Line Items]
Assets	11,880	11,701
Equity securities [Member] | Non-redeemable preferred stock | Level 1 [Member]
Fair Value Measurement [Line Items]
Assets	0	0
Equity securities [Member] | Non-redeemable preferred stock | Level 2 [Member]
Fair Value Measurement [Line Items]
Assets	11,880	11,701
Equity securities [Member] | Non-redeemable preferred stock | Level 3 [Member]
Fair Value Measurement [Line Items]
Assets	0	0
Equity securities [Member] | Partnership interest in private credit fund [Member]
Fair Value Measurement [Line Items]
Assets	11,592	11,306
Equity securities [Member] | Partnership interest in private credit fund [Member] | Level 1 [Member]
Fair Value Measurement [Line Items]
Assets	0	0
Equity securities [Member] | Partnership interest in private credit fund [Member] | Level 2 [Member]
Fair Value Measurement [Line Items]
Assets	0	0
Equity securities [Member] | Partnership interest in private credit fund [Member] | Level 3 [Member]
Fair Value Measurement [Line Items]
Assets	$ 11,592	$ 11,306