Investments (Components Of Net Investment Income) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Schedule of Available-for-sale Securities [Line Items]
Total gross investment income	$ 640,437	$ 666,235	$ 561,389
Interest debited (credited) and other investment expense	(20,396)	(12,772)	(13,596)
Net investment income	620,041	653,463	547,793
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total gross investment income	57,573	12,200	3,574
Fixed Maturity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total gross investment income	521,991	581,870	570,798
Short-Term Investments And Cash [Member]
Schedule of Available-for-sale Securities [Line Items]
Total gross investment income	1,281	151	5,965
Limited Partnerships [Member]
Schedule of Available-for-sale Securities [Line Items]
Total gross investment income	56,851	70,740	(19,022)
Other [Member]
Schedule of Available-for-sale Securities [Line Items]
Total gross investment income	$ 2,741	$ 1,274	$ 74