Investments (Components Of Net Investment Income) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Municipal bonds (tax-exempt)	$ 22,758	$ 22,563	$ 45,130	$ 44,485
Short-term investments, including overnight deposits	5,834	2,654	10,783	4,945
Dividends on equity securities	19,017	16,758	39,623	34,410
Income from equity method investments	1,802	3,921	6,395	3,668
Other	24	190	(205)	2,674
Total investment income	103,524	99,267	208,208	194,570
Investment expenses	(4,225)	(4,271)	(8,541)	(8,280)
Net investment income	99,299	94,996	199,667	186,290
Taxable Municipal Bonds [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Taxable bonds	17,793	16,222	35,298	32,110
Other Taxable Bonds [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Taxable bonds	$ 36,296	$ 36,959	$ 71,184	$ 72,278