Condensed Financial Information of Registrant (Schedule Of Condensed Financial Information Of Registrant, Statements Of Cash Flow) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net cash provided by operating activities	$ 605,616,000	$ 519,678,000	$ 383,434,000
Cash flows from investing activities:
Capital distribution from subsidiaries	12,100,000	5,200,000
Equity securities available for sale in nature
Purchases	(1,230,785,000)	(1,174,759,000)	(1,026,827,000)
Sales	1,174,540,000	1,088,701,000	954,755,000
Other, net	20,577,000	6,247,000	10,105,000
Net cash used in investing activities	(411,286,000)	(401,201,000)	(222,436,000)
Cash flows from financing activities:
Dividends paid to shareholders	(139,640,000)	(139,071,000)	(138,478,000)
Proceeds from stock options exercised	0	701,000	358,000
Net cash used in financing activities	(140,249,000)	(138,370,000)	(138,120,000)
Net (decrease) increase in cash	54,081,000	(19,893,000)	22,878,000
Cash:
Beginning of year	294,398,000	314,291,000	291,413,000
End of year	348,479,000	294,398,000	314,291,000
SUPPLEMENTAL CASH FLOW DISCLOSURE
Interest paid	16,599,000	16,586,000	16,586,000
Income taxes (refunded) paid, net	52,659,000	(14,564,000)	(10,989,000)
Parent Company [Member]
Cash flows from operating activities:
Net cash provided by operating activities	(17,339,000)	(5,392,000)	(16,108,000)
Cash flows from investing activities:
Capital contribution to subsidiaries	(30,000,000)	(125,000)	(540,619)
Capital distribution from subsidiaries	0	30,068,567	0
Distributions received from special purpose entities	12,129,000	5,153,000	5,998,000
Dividends received from subsidiaries	121,000,000	114,431,000	135,000,000
Equity securities available for sale in nature
Purchases	(54,571,000)	(39,966,000)	(22,286,000)
Sales	67,965,000	74,663,000	33,052,000
Decrease (increase) in short-term investments	25,088,000	(25,213,000)	18,065,000
Other, net	254,000	376,000	605,000
Net cash used in investing activities	141,865,000	159,388,000	169,893,000
Cash flows from financing activities:
Dividends paid to shareholders	(139,640,000)	(139,071,000)	(138,478,000)
Proceeds from stock options exercised	0	701,000	358,000
Net cash used in financing activities	(139,640,000)	(138,370,000)	(138,120,000)
Net (decrease) increase in cash	(15,114,000)	15,626,000	15,665,000
Cash:
Beginning of year	39,766,000	24,140,000	8,475,000
End of year	24,652,000	39,766,000	24,140,000
SUPPLEMENTAL CASH FLOW DISCLOSURE
Interest paid	16,586,000	16,586,000	16,586,000
Income taxes (refunded) paid, net	$ (20,552,000)	$ (12,391,000)	$ 4,296,000