Investments (Components Of Net Investment Income) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Document Period End Date			Jun. 30, 2019
Municipal bonds (tax-exempt)	$ 17,885	$ 20,287	$ 36,711	$ 41,222
Short-term investments, including overnight deposits	13,753	11,915	23,965	22,505
Dividends on equity securities	22,207	20,474	47,993	44,481
Income from equity method investments	1,174	(1,490)	3,070	288
Other	873	97	3,174	(13)
Total investment income	115,747	109,051	234,128	221,353
Investment expenses	(3,916)	(3,664)	(8,115)	(7,950)
Net investment income	111,831	105,387	226,013	213,403
Taxable Municipal Bonds [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Taxable bonds	18,613	18,220	37,192	35,853
Other Taxable Bonds [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Taxable bonds	$ 41,242	$ 39,548	$ 82,023	$ 77,017