Investments (Components Of Net Investment Income) (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Municipal bonds (tax-exempt)	$ 16,157	$ 17,885	$ 32,758	$ 36,711
Short-term investments, including overnight deposits	2,379	13,753	12,622	23,965
Dividends on equity securities	18,020	22,207	46,634	47,993
Income (loss) from equity method investments	5,647	1,174	(14,332)	3,070
Other	46	873	803	3,174
Total investment income	98,699	115,747	191,802	234,128
Investment expenses	(3,084)	(3,916)	(7,944)	(8,115)
Net investment income	95,615	111,831	183,858	226,013
Municipal Bonds (taxable) [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Taxable bonds	16,834	18,613	33,729	37,192
Other taxable bonds [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Taxable bonds	$ 39,616	$ 41,242	$ 79,588	$ 82,023

Amount of income (loss) for proportionate share of equity method investee's income (loss).

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