Investments (Components Of Net Investment Income) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Municipal bonds (tax-exempt)	$ 71,351	$ 80,016	$ 87,768
Short-term investments, including overnight deposits	50,425	48,765	26,772
Dividends on equity securities	100,222	90,840	82,096
Income (loss) from equity method investments	4,368	(1,924)	11,076
Other	(5,338)	(881)	(828)
Total investment income	467,383	450,965	422,740
Investment expenses	(15,495)	(16,750)	(17,031)
Net investment income	451,888	434,215	405,709
Taxable municipal bonds [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Taxable bonds	72,818	73,058	70,771
Other taxable bonds [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Taxable bonds	$ 162,861	$ 159,329	$ 145,085