Condensed Financial Information of Registrant (Schedule Of Condensed Financial Information Of Registrant, Balance Sheets) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Investments, at fair value:
Short-term investments (cost $29,356; $3,166)	$ 494,135	$ 253,299
Total investments	4,312,161	3,768,091
Cash	294,398	314,291	$ 291,413	$ 220,318
Accrued investment income	40,107	45,373
Current income taxes	7,642	38,885
Other assets	44,247	45,008
Total assets	5,889,157	5,433,729
Liabilities
Notes payable	372,133	371,734
Accounts payable and accrued expenses	143,318	115,071
Deferred income taxes	27,964	0
Other liabilities	221,442	263,647
Total liabilities	4,089,655	3,816,045
Shareholders’ equity:
Common stock	98,828	98,026
Retained earnings	1,700,674	1,519,658
Total shareholders’ equity	1,799,502	1,617,684	1,761,387
Total liabilities and shareholders’ equity	5,889,157	5,433,729
Cost - equity security trading investments	648,282	544,082
Cost - short-term investments	494,060	254,518
Parent Company [Member]
Investments, at fair value:
Equity securities (cost $81,802; $110,279)	114,668	119,037
Short-term investments (cost $29,356; $3,166)	29,356	3,166
Investment in subsidiaries	2,008,163	1,850,582
Total investments	2,152,187	1,972,785
Cash	39,766	24,140	$ 8,475	$ 11,786
Accrued investment income	90	161
Amounts receivable from affiliates	244	1,172
Current income taxes	0	0
Income tax receivable from affiliates	9,192	19,225
Other assets	312	446
Total assets	2,201,791	2,017,929
Liabilities
Notes payable	372,133	371,734
Accounts payable and accrued expenses	17	25
Amounts payable to affiliates	22	3,082
Income tax payable to affiliates	4,106	580
Current income taxes	14,052	17,773
Deferred income taxes	7,059	1,691
Other liabilities	4,900	5,360
Total liabilities	402,289	400,245
Shareholders’ equity:
Common stock	98,828	98,026
Retained earnings	1,700,674	1,519,658
Total shareholders’ equity	1,799,502	1,617,684
Total liabilities and shareholders’ equity	2,201,791	2,017,929
Cost - equity security trading investments	81,802	110,279
Cost - short-term investments	$ 29,356	$ 3,166