Condensed Financial Information of Registrant (Schedule Of Condensed Financial Information Of Registrant, Balance Sheets) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Investments, at fair value:
Short-term investments (cost $3,166; $21,233)	$ 253,299	$ 302,711
Total investments	3,768,091	3,732,728
Cash	314,291	291,413	$ 220,318	$ 264,221
Accrued investment income	45,373	39,368
Current income taxes	38,885	61,257
Other assets	45,008	32,592
Total assets	5,433,729	5,101,323
Liabilities
Notes payable	371,734	371,335
Accounts payable and accrued expenses	115,071	108,252
Deferred income taxes	0	22,932
Other liabilities	263,647	224,877
Total liabilities	3,816,045	3,339,936
Shareholders’ equity:
Common stock	98,026	97,523
Retained earnings	1,519,658	1,663,864
Total shareholders’ equity	1,617,684	1,761,387	1,752,402
Total liabilities and shareholders’ equity	5,433,729	5,101,323
Cost - equity security trading investments	544,082	474,197
Cost - short-term investments	254,518	302,693
Parent Company [Member]
Investments, at fair value:
Equity securities (cost $110,279; $113,216)	119,037	141,227
Short-term investments (cost $3,166; $21,233)	3,166	21,231
Investment in subsidiaries	1,850,582	1,976,400
Total investments	1,972,785	2,138,858
Cash	24,140	8,475	$ 11,786	$ 20,139
Accrued investment income	161	178
Amounts receivable from affiliates	1,172	231
Current income taxes	0	8,857
Income tax receivable from affiliates	19,225	6,338
Other assets	446	663
Total assets	2,017,929	2,163,600
Liabilities
Notes payable	371,734	371,335
Accounts payable and accrued expenses	25	0
Amounts payable to affiliates	3,082	507
Income tax payable to affiliates	580	17,213
Current income taxes	17,773	0
Deferred income taxes	1,691	8,242
Other liabilities	5,360	4,916
Total liabilities	400,245	402,213
Shareholders’ equity:
Common stock	98,026	97,523
Retained earnings	1,519,658	1,663,864
Total shareholders’ equity	1,617,684	1,761,387
Total liabilities and shareholders’ equity	2,017,929	2,163,600
Cost - equity security trading investments	110,279	113,216
Cost - short-term investments	$ 3,166	$ 21,233