Fair Value Measurement (Schedule Of Assets And Liabilities Measured At Fair Value On A Recurring Basis Valuation Techniques) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities:	$ 3,485,363	$ 3,093,275
Equity securities:	809,591	724,751
Short-term investments:	253,842	494,135
Equity contracts [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative liability	1,356	77
Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities:	3,485,363	3,093,275
Equity securities:	809,591	724,751
Short-term investments:	253,842	494,135
Note receivable	5,736	5,665
Assets, fair value disclosure	4,554,532	4,317,826
Liabilities, fair value	1,356	77
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities:	24,233	22,637
Equity securities:	705,359	586,367
Short-term investments:	238,837	464,055
Note receivable	0	0
Assets, fair value disclosure	968,429	1,073,059
Liabilities, fair value	1,356	77
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities:	3,461,130	3,070,638
Equity securities:	31,677	49,708
Short-term investments:	15,005	30,080
Note receivable	5,736	5,665
Assets, fair value disclosure	3,513,548	3,156,091
Liabilities, fair value	0	0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities:	0	0
Equity securities:	0	1,203
Short-term investments:	0	0
Note receivable	0	0
Assets, fair value disclosure	0	1,203
Liabilities, fair value	0	0
Fair Value, Measurements, Recurring [Member] | US Government Agencies Debt Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities:	24,233	22,637
Fair Value, Measurements, Recurring [Member] | US Government Agencies Debt Securities [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities:	24,233	22,637
Fair Value, Measurements, Recurring [Member] | US Government Agencies Debt Securities [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities:	0	0
Fair Value, Measurements, Recurring [Member] | US Government Agencies Debt Securities [Member] | Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities:	0	0
Fair Value, Measurements, Recurring [Member] | Municipal Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities:	2,773,691	2,554,208
Fair Value, Measurements, Recurring [Member] | Municipal Securities [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities:	0	0
Fair Value, Measurements, Recurring [Member] | Municipal Securities [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities:	2,773,691	2,554,208
Fair Value, Measurements, Recurring [Member] | Municipal Securities [Member] | Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities:	0	0
Fair Value, Measurements, Recurring [Member] | Mortgage Backed Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities:	70,366	63,003
Fair Value, Measurements, Recurring [Member] | Mortgage Backed Securities [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities:	0	0
Fair Value, Measurements, Recurring [Member] | Mortgage Backed Securities [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities:	70,366	63,003
Fair Value, Measurements, Recurring [Member] | Mortgage Backed Securities [Member] | Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities:	0	0
Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities:	251,138	235,565
Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities:	0	0
Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities:	251,138	235,565
Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member] | Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities:	0	0
Fair Value, Measurements, Recurring [Member] | Collateralized Loan Obligations [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities:	257,004	199,217
Fair Value, Measurements, Recurring [Member] | Collateralized Loan Obligations [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities:	0	0
Fair Value, Measurements, Recurring [Member] | Collateralized Loan Obligations [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities:	257,004	199,217
Fair Value, Measurements, Recurring [Member] | Collateralized Loan Obligations [Member] | Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities:	0	0
Fair Value, Measurements, Recurring [Member] | Other Asset-Backed Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities:	108,931	18,645
Fair Value, Measurements, Recurring [Member] | Other Asset-Backed Securities [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities:	0	0
Fair Value, Measurements, Recurring [Member] | Other Asset-Backed Securities [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities:	108,931	18,645
Fair Value, Measurements, Recurring [Member] | Other Asset-Backed Securities [Member] | Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities:	0	0
Fair Value, Measurements, Recurring [Member] | Common Stock [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity securities:	705,359	586,367
Fair Value, Measurements, Recurring [Member] | Common Stock [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity securities:	705,359	586,367
Fair Value, Measurements, Recurring [Member] | Common Stock [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity securities:	0	0
Fair Value, Measurements, Recurring [Member] | Common Stock [Member] | Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity securities:	0	0
Fair Value, Measurements, Recurring [Member] | Nonredeemable Preferred Stock [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity securities:	31,677	49,708
Fair Value, Measurements, Recurring [Member] | Nonredeemable Preferred Stock [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity securities:	0	0
Fair Value, Measurements, Recurring [Member] | Nonredeemable Preferred Stock [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity securities:	31,677	49,708
Fair Value, Measurements, Recurring [Member] | Nonredeemable Preferred Stock [Member] | Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity securities:	0	0
Fair Value, Measurements, Recurring [Member] | Private Equity Funds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity securities:		1,203
Fair Value, Measurements, Recurring [Member] | Private Equity Funds [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity securities:		0
Fair Value, Measurements, Recurring [Member] | Private Equity Funds [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity securities:		0
Fair Value, Measurements, Recurring [Member] | Private Equity Funds [Member] | Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity securities:		1,203
Fair Value, Measurements, Recurring [Member] | Private Equity Funds Net Asset Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity securities:	72,555	87,473
Fair Value, Measurements, Recurring [Member] | Short-term Debt [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments:	15,005	32,902
Fair Value, Measurements, Recurring [Member] | Short-term Debt [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments:	0	2,822
Fair Value, Measurements, Recurring [Member] | Short-term Debt [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments:	15,005	30,080
Fair Value, Measurements, Recurring [Member] | Short-term Debt [Member] | Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments:	0	0
Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments:	238,837	461,233
Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments:	238,837	461,233
Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments:	0	0
Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member] | Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments:	0	0
Fair Value, Measurements, Recurring [Member] | Equity contracts [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative liability	1,356	77
Fair Value, Measurements, Recurring [Member] | Equity contracts [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative liability	0	0
Fair Value, Measurements, Recurring [Member] | Equity contracts [Member] | Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative liability	$ 0	$ 0