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
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.