Condensed Financial Information of Registrant (Schedule Of Condensed Financial Information Of Registrant, Balance Sheets) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Investments, at fair value:
Equity securities	$ 477,088	$ 380,388
Short-term investments	294,653	236,444
Total investments	3,180,095	3,062,421
Cash	158,183	211,393	181,388	185,505
Accrued investment income	31,109	32,541
Current income taxes	7,058	0
Deferred income taxes	0	6,511
Total assets	4,189,686	4,070,006
LIABILITIES AND SHAREHOLDERS’ EQUITY
Accounts payable and accrued expenses	96,220	94,743
Deferred income taxes	445	0
Other liabilities	153,972	149,007
Total liabilities	2,347,189	2,212,523
Shareholders’ equity:
Common stock	79,380	76,634
Additional paid -in capital	0	538
Retained earnings	1,763,117	1,780,311
Total shareholders’ equity	1,842,497	1,857,483	1,794,815
Total liabilities and shareholders’ equity	4,189,686	4,070,006
Parent Company [Member]
Investments, at fair value:
Equity securities	27,127	20,282
Short-term investments	47,174	26,817
Investment in subsidiaries	1,760,760	1,787,047
Total investments	1,835,061	1,834,146
Cash	10,199	29,219	41,606	45,344
Accrued investment income	4	17
Amounts receivable from affiliates	200	200
Current income taxes	6,333	22
Deferred income taxes	729	1,654
Income tax receivable from affiliates	6,182	12,833
Total assets	1,858,708	1,878,091
LIABILITIES AND SHAREHOLDERS’ EQUITY
Accounts payable and accrued expenses	47	48
Amounts payable to affiliates	95	0
Income tax payable to affiliates	16,069	20,288
Other liabilities	0	272
Total liabilities	16,211	20,608
Shareholders’ equity:
Common stock	79,380	76,634
Additional paid -in capital	0	538
Retained earnings	1,763,117	1,780,311
Total shareholders’ equity	1,842,497	1,857,483
Total liabilities and shareholders’ equity	1,858,708	1,878,091
Equity securities trading - cost	31,178	24,885
Short-term investments - cost	$ 47,174	$ 26,817