Fair Value Measurement (Schedule Of Assets And Liabilities Measured At Fair Value On A Recurring Basis Valuation Techniques) (Details) - USD ($) $ in Thousands | Jun. 30, 2015 | Dec. 31, 2014 |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | $ 3,359,767 | $ 3,403,822 |
Liabilities, Fair Value Disclosure, Recurring | 1,615 | 4,219 |
Level 1 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 451,840 | 742,886 |
Liabilities, Fair Value Disclosure, Recurring | 51 | 194 |
Level 2 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 2,894,182 | 2,649,217 |
Liabilities, Fair Value Disclosure, Recurring | 1,564 | 4,025 |
Level 3 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 13,745 | 11,719 |
Liabilities, Fair Value Disclosure, Recurring | 0 | 0 |
Fixed maturity securities [Member] | US Treasury and Government [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 24,783 | 16,108 |
Fixed maturity securities [Member] | US Treasury and Government [Member] | Level 1 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 24,783 | 16,108 |
Fixed maturity securities [Member] | US Treasury and Government [Member] | Level 2 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 0 | 0 |
Fixed maturity securities [Member] | US Treasury and Government [Member] | Level 3 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 0 | 0 |
Fixed maturity securities [Member] | US States and Political Subdivisions Debt Securities [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 2,486,708 | 2,275,455 |
Fixed maturity securities [Member] | US States and Political Subdivisions Debt Securities [Member] | Level 1 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 0 | 0 |
Fixed maturity securities [Member] | US States and Political Subdivisions Debt Securities [Member] | Level 2 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 2,486,708 | 2,275,455 |
Fixed maturity securities [Member] | US States and Political Subdivisions Debt Securities [Member] | Level 3 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 0 | 0 |
Fixed maturity securities [Member] | Collateralized Mortgage Backed Securities [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 59,091 | 47,691 |
Fixed maturity securities [Member] | Collateralized Mortgage Backed Securities [Member] | Level 1 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 0 | 0 |
Fixed maturity securities [Member] | Collateralized Mortgage Backed Securities [Member] | Level 2 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 59,091 | 47,691 |
Fixed maturity securities [Member] | Collateralized Mortgage Backed Securities [Member] | Level 3 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 0 | 0 |
Fixed maturity securities [Member] | Corporate Debt Securities [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 269,384 | 256,930 |
Fixed maturity securities [Member] | Corporate Debt Securities [Member] | Level 1 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 0 | 0 |
Fixed maturity securities [Member] | Corporate Debt Securities [Member] | Level 2 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 269,384 | 256,930 |
Fixed maturity securities [Member] | Corporate Debt Securities [Member] | Level 3 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 0 | 0 |
Fixed maturity securities [Member] | Collateralized Debt Obligations [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 50,663 | 22,216 |
Fixed maturity securities [Member] | Collateralized Debt Obligations [Member] | Level 1 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 0 | 0 |
Fixed maturity securities [Member] | Collateralized Debt Obligations [Member] | Level 2 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 50,663 | 22,216 |
Fixed maturity securities [Member] | Collateralized Debt Obligations [Member] | Level 3 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 0 | 0 |
Equity Securities [Member] | Public Utility, Equities [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 73,704 | 105,485 |
Equity Securities [Member] | Public Utility, Equities [Member] | Level 1 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 73,704 | 105,485 |
Equity Securities [Member] | Public Utility, Equities [Member] | Level 2 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 0 | 0 |
Equity Securities [Member] | Public Utility, Equities [Member] | Level 3 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 0 | 0 |
Equity Securities [Member] | Banks, Trust and Insurance, Equities [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 11,090 | 9,757 |
Equity Securities [Member] | Banks, Trust and Insurance, Equities [Member] | Level 1 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 11,090 | 9,757 |
Equity Securities [Member] | Banks, Trust and Insurance, Equities [Member] | Level 2 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 0 | 0 |
Equity Securities [Member] | Banks, Trust and Insurance, Equities [Member] | Level 3 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 0 | 0 |
Equity Securities [Member] | Industrial, Miscellaneous, and All Others [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 190,882 | 257,356 |
Equity Securities [Member] | Industrial, Miscellaneous, and All Others [Member] | Level 1 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 190,882 | 257,356 |
Equity Securities [Member] | Industrial, Miscellaneous, and All Others [Member] | Level 2 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 0 | 0 |
Equity Securities [Member] | Industrial, Miscellaneous, and All Others [Member] | Level 3 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 0 | 0 |
Equity Securities [Member] | Nonredeemable Preferred Stock [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 26,169 | 28,563 |
Equity Securities [Member] | Nonredeemable Preferred Stock [Member] | Level 1 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 0 | 0 |
Equity Securities [Member] | Nonredeemable Preferred Stock [Member] | Level 2 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 26,169 | 28,563 |
Equity Securities [Member] | Nonredeemable Preferred Stock [Member] | Level 3 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 0 | 0 |
Equity Securities [Member] | Partnership Interest In Private Credit Fund [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 13,745 | 11,719 |
Equity Securities [Member] | Partnership Interest In Private Credit Fund [Member] | Level 1 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 0 | 0 |
Equity Securities [Member] | Partnership Interest In Private Credit Fund [Member] | Level 2 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 0 | 0 |
Equity Securities [Member] | Partnership Interest In Private Credit Fund [Member] | Level 3 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 13,745 | 11,719 |
Short-term Investments [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 72,163 | 88,361 |
Short-term Investments [Member] | Level 1 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 69,996 | 69,999 |
Short-term Investments [Member] | Level 2 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 2,167 | 18,362 |
Short-term Investments [Member] | Level 3 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 0 | 0 |
Money Market Funds [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 81,385 | 284,181 |
Money Market Funds [Member] | Level 1 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 81,385 | 284,181 |
Money Market Funds [Member] | Level 2 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 0 | 0 |
Money Market Funds [Member] | Level 3 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Assets, Fair Value Disclosure, Recurring | 0 | 0 |
Total Return Swap [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Liabilities, Fair Value Disclosure, Recurring | 1,564 | 4,025 |
Total Return Swap [Member] | Level 1 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Liabilities, Fair Value Disclosure, Recurring | 0 | 0 |
Total Return Swap [Member] | Level 2 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Liabilities, Fair Value Disclosure, Recurring | 1,564 | 4,025 |
Total Return Swap [Member] | Level 3 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Liabilities, Fair Value Disclosure, Recurring | 0 | 0 |
Equity Contract [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Liabilities, Fair Value Disclosure, Recurring | 51 | 194 |
Equity Contract [Member] | Level 1 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Liabilities, Fair Value Disclosure, Recurring | 51 | 194 |
Equity Contract [Member] | Level 2 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Liabilities, Fair Value Disclosure, Recurring | 0 | 0 |
Equity Contract [Member] | Level 3 [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Liabilities, Fair Value Disclosure, Recurring | $ 0 | $ 0 |