Investments (Components Of Net Investment Income) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Municipal bonds (tax-exempt)	$ 80,016	$ 87,768	$ 88,654
Short-term investments, including overnight deposits	48,765	26,772	11,177
Dividends on equity securities	90,840	82,096	70,577
Income (loss) from equity method investments	(1,924)	11,076	6,852
Other	881	(828)	2,676
Total investment income	450,965	422,740	390,437
Investment expenses	(16,750)	(17,031)	(17,207)
Net investment income	434,215	405,709	373,230
Taxable Municipal Bonds [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Taxable bonds	73,058	70,771	65,749
Other Taxable Bonds [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Taxable bonds	$ 159,329	$ 145,085	$ 144,752