Fair Value Measurement (Schedule Of Assets And Liabilities Measured At Fair Value On A Recurring Basis Valuation Techniques) (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities:	$ 3,761,777	$ 3,549,810
Equity securities:	870,556	803,851
Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities:	3,761,777	3,549,810
Equity securities:	870,556	803,851
Short-term investments:	408,471	375,609
Note receivable	5,698	5,725
Assets, fair value disclosure	5,046,502	4,734,995
Liabilities	167
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities:	14,279	13,816
Equity securities:	733,546	691,782
Short-term investments:	403,461	370,680
Note receivable	0	0
Assets, fair value disclosure	1,151,286	1,076,278
Liabilities	167
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities:	3,747,498	3,535,994
Equity securities:	54,211	32,660
Short-term investments:	5,010	4,929
Note receivable	5,698	5,725
Assets, fair value disclosure	3,812,417	3,579,308
Liabilities	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	0
Short-term investments:	0	0
Note receivable	0	0
Assets, fair value disclosure	0	0
Liabilities	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:	14,279	13,816
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:	14,279	13,816
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:	2,845,983	2,791,212
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:	2,845,983	2,791,212
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:	92,548	93,264
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:	92,548	93,264
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:	283,407	241,366
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:	283,407	241,366
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:	278,336	256,891
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:	278,336	256,891
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:	247,224	153,261
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:	247,224	153,261
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:	733,546	691,782
Fair Value, Measurements, Recurring [Member] | Common Stock [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity securities:	733,546	691,782
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:	54,211	32,660
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:	54,211	32,660
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 Net Asset Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity securities:	82,799	79,409
Fair Value, Measurements, Recurring [Member] | Short-term Debt [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments:	5,010	26,928
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	21,999
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:	5,010	4,929
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:	403,451	348,676
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:	403,451	348,676
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] | Other Short-term Investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments:	10	5
Fair Value, Measurements, Recurring [Member] | Other Short-term Investments | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments:	10	5
Fair Value, Measurements, Recurring [Member] | Other Short-term Investments | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments:	0	0
Fair Value, Measurements, Recurring [Member] | Other Short-term Investments | 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]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative liability	167
Fair Value, Measurements, Recurring [Member] | Equity contracts [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative liability	167
Fair Value, Measurements, Recurring [Member] | Equity contracts [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative liability	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