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Fair Value Measurement (Schedule Of Assets And Liabilities Measured At Fair Value On A Recurring Basis Valuation Techniques) (Details) - USD ($) $ in Thousands | Dec. 31, 2016 | Dec. 31, 2015
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Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | $ 3,548,227 | $ 3,380,642
Fair value of liabilities measured on a recurring basis |  | 320,785 | 301,785
Level 1 [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 684,172 | 478,197
Fair value of liabilities measured on a recurring basis |  | 20 | 260
Level 2 [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 2,854,987 | 2,892,014
Fair value of liabilities measured on a recurring basis |  | 320,765 | 301,525
Level 3 [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 9,068 | 10,431
Fair value of liabilities measured on a recurring basis |  | 0 | 0
Fixed Maturity Securities [Member] | US Treasury and Government [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 12,275 | 22,507
Fixed Maturity Securities [Member] | US Treasury and Government [Member] | Level 1 [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 12,275 | 22,507
Fixed Maturity Securities [Member] | US Treasury and Government [Member] | Level 2 [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 0 | 0
Fixed Maturity Securities [Member] | US Treasury and Government [Member] | Level 3 [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 0 | 0
Fixed Maturity Securities [Member] | US States and Political Subdivisions Debt Securities [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 2,449,292 | 2,505,040
Fixed Maturity Securities [Member] | US States and Political Subdivisions Debt Securities [Member] | Level 1 [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 0 | 0
Fixed Maturity Securities [Member] | US States and Political Subdivisions Debt Securities [Member] | Level 2 [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 2,449,292 | 2,505,040
Fixed Maturity Securities [Member] | US States and Political Subdivisions Debt Securities [Member] | Level 3 [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 0 | 0
Fixed Maturity Securities [Member] | Collateralized Mortgage Backed Securities [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 39,777 | 49,838
Fixed Maturity Securities [Member] | Collateralized Mortgage Backed Securities [Member] | Level 1 [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 0 | 0
Fixed Maturity Securities [Member] | Collateralized Mortgage Backed Securities [Member] | Level 2 [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 39,777 | 49,838
Fixed Maturity Securities [Member] | Collateralized Mortgage Backed Securities [Member] | Level 3 [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 0 | 0
Fixed Maturity Securities [Member] | Corporate Debt Securities [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 189,688 | 243,372
Fixed Maturity Securities [Member] | Corporate Debt Securities [Member] | Level 1 [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 0 | 0
Fixed Maturity Securities [Member] | Corporate Debt Securities [Member] | Level 2 [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 189,688 | 243,372
Fixed Maturity Securities [Member] | Corporate Debt Securities [Member] | Level 3 [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 0 | 0
Fixed Maturity Securities [Member] | Collateralized Debt Obligations [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 86,525 | 50,548
Fixed Maturity Securities [Member] | Collateralized Debt Obligations [Member] | Level 1 [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 0 | 0
Fixed Maturity Securities [Member] | Collateralized Debt Obligations [Member] | Level 2 [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 86,525 | 50,548
Fixed Maturity Securities [Member] | Collateralized Debt Obligations [Member] | Level 3 [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 0 | 0
Fixed Maturity Securities [Member] | Collateralized Auto Loans [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 36,996 | 8,698
Fixed Maturity Securities [Member] | Collateralized Auto Loans [Member] | Level 1 [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 0 | 0
Fixed Maturity Securities [Member] | Collateralized Auto Loans [Member] | Level 2 [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 36,996 | 8,698
Fixed Maturity Securities [Member] | Collateralized Auto Loans [Member] | Level 3 [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 0 | 0
Equity Securities [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 316,450 | 280,263
Equity Securities [Member] | Level 1 [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 316,450 | 280,263
Equity Securities [Member] | Level 2 [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 0 | 0
Equity Securities [Member] | Level 3 [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 0 | 0
Equity Securities [Member] | Nonredeemable Preferred Stock [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 31,809 | 24,668
Equity Securities [Member] | Nonredeemable Preferred Stock [Member] | Level 1 [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 0 | 0
Equity Securities [Member] | Nonredeemable Preferred Stock [Member] | Level 2 [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 31,809 | 24,668
Equity Securities [Member] | Nonredeemable Preferred Stock [Member] | Level 3 [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 0 | 0
Equity Securities [Member] | Private Equity Funds [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 9,068 | 10,431
Equity Securities [Member] | Private Equity Funds [Member] | Level 1 [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 0 | 0
Equity Securities [Member] | Private Equity Funds [Member] | Level 2 [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 0 | 0
Equity Securities [Member] | Private Equity Funds [Member] | Level 3 [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 9,068 | 10,431
Short-term Investments [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 90,626 | 79,841
Short-term Investments [Member] | Level 1 [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 70,393 | 69,991
Short-term Investments [Member] | Level 2 [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 20,233 | 9,850
Short-term Investments [Member] | Level 3 [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 0 | 0
Money Market Funds [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 285,054 | 105,436
Money Market Funds [Member] | Level 1 [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 285,054 | 105,436
Money Market Funds [Member] | Level 2 [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 0 | 0
Money Market Funds [Member] | Level 3 [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 0 | 0
Total Return Swap [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 667 |
Fair value of liabilities measured on a recurring basis |  | 765 | 11,525
Total Return Swap [Member] | Level 1 [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 0 |
Fair value of liabilities measured on a recurring basis |  | 0 | 0
Total Return Swap [Member] | Level 2 [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 667 |
Fair value of liabilities measured on a recurring basis |  | 765 | 11,525
Total Return Swap [Member] | Level 3 [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of assets measured on a recurring basis |  | 0 |
Fair value of liabilities measured on a recurring basis |  | 0 | 0
Equity Contract [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of liabilities measured on a recurring basis |  | 20 | 260
Equity Contract [Member] | Level 1 [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of liabilities measured on a recurring basis |  | 20 | 260
Equity Contract [Member] | Level 2 [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of liabilities measured on a recurring basis |  | 0 | 0
Equity Contract [Member] | Level 3 [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of liabilities measured on a recurring basis |  | 0 | 0
Secured Debt [Member] | Borrowings [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of liabilities measured on a recurring basis |  | 140,000 | 140,000
Secured Debt [Member] | Borrowings [Member] | Level 1 [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of liabilities measured on a recurring basis |  | 0 | 0
Secured Debt [Member] | Borrowings [Member] | Level 2 [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of liabilities measured on a recurring basis |  | 140,000 | 140,000
Secured Debt [Member] | Borrowings [Member] | Level 3 [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of liabilities measured on a recurring basis |  | 0 | 0
Unsecured Debt [Member] | Borrowings [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of liabilities measured on a recurring basis |  | 180,000 | 150,000
Unsecured Debt [Member] | Borrowings [Member] | Level 1 [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of liabilities measured on a recurring basis |  | 0 | 0
Unsecured Debt [Member] | Borrowings [Member] | Level 2 [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of liabilities measured on a recurring basis | [1] | 180,000 | 150,000
Unsecured Debt [Member] | Borrowings [Member] | Level 3 [Member] |  |  |
Fair Value Measurement [Line Items] |  |  |
Fair value of liabilities measured on a recurring basis |  | $ 0 | $ 0
[1] | On July 2, 2013, the Company entered into an unsecured $200 million five-year revolving credit facility, which later was expanded to a borrowing capacity of $250 million. The interest rate on borrowings under the credit facility is based on the Company's debt to total capital ratio and ranges from LIBOR plus 112.5 basis points when the ratio is under 15% to LIBOR plus 162.5 basis points when the ratio is above 25%. Commitment fees for the undrawn portions of the credit facility range from 12.5 basis points when the ratio is under 15% to 22.5 basis points when the ratio is above 25%. Debt to capital ratio is expressed as a percentage of (a) consolidated debt to (b) consolidated shareholders' equity plus consolidated debt. In 2016, the interest rate was LIBOR plus 112.5 basis points on the $180 million of borrowings and 12.5 basis points on the undrawn portion of the credit facility. The interest rate was approximately 1.73% at December 31, 2016.

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- Definition This element represents the aggregate of the assets reported on the balance sheet at period end measured at fair value on a recurring basis by the entity. This element is intended to be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. + References No definition available. + Details
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