Condensed Financial Information of Registrant (Schedule Of Condensed Financial Information Of Registrant, Balance Sheets) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Investments, at fair value:
Equity securities (cost $189,032; $27,449)	$ 412,880	$ 281,883
Short-term investments (cost $9,744; $11,089)	372,542	315,776
Total investments	3,403,822	3,158,312
Cash	289,907	266,508	158,183	211,393
Accrued investment income	38,737	36,120
Current income taxes	503	0
Deferred income taxes	0	15,220
Other assets	21,512	14,336
Total assets	4,600,289	4,315,181
Liabilities:
Notes payable	290,000	190,000
Accounts payable and accrued expenses	130,887	127,663
Current income taxes	0	11,856
Deferred income taxes	5,333	0
Other liabilities	207,028	170,665
Total liabilities	2,724,843	2,492,695
Shareholders’ equity:
Common stock	88,705	81,591
Additional paid-in capital	3,804	411
Retained earnings	1,782,937	1,740,484
Total shareholders’ equity	1,875,446	1,822,486	1,842,497
Total liabilities and shareholders’ equity	4,600,289	4,315,181
Parent Company [Member]
Investments, at fair value:
Equity securities (cost $189,032; $27,449)	182,300	29,737
Short-term investments (cost $9,744; $11,089)	9,744	11,089
Investment in subsidiaries	1,783,049	1,794,164
Total investments	1,975,093	1,834,990
Cash	52,326	46,332	10,199	29,219
Accrued investment income	158	16
Amounts receivable from affiliates	1,181	206
Current income taxes	239	0
Deferred income taxes	6,975	1,068
Income tax receivable from affiliates	3,482	11,573
Other assets	1,095	459
Total assets	2,040,549	1,894,644
Liabilities:
Notes payable	150,000	50,000
Accounts payable and accrued expenses	0	23
Amounts payable to affiliates	97	34
Income tax payable to affiliates	14,728	6,730
Current income taxes	0	12,672
Other liabilities	278	2,699
Total liabilities	165,103	72,158
Shareholders’ equity:
Common stock	88,705	81,591
Additional paid-in capital	3,804	411
Retained earnings	1,782,937	1,740,484
Total shareholders’ equity	1,875,446	1,822,486
Total liabilities and shareholders’ equity	2,040,549	1,894,644
Equity securities trading - cost	189,032	27,499
Short-term investments - cost	$ 9,744	$ 11,089