Supplemental Financial Statement Information (Schedule of Other Operating Cost and Expense, by Component) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Supplemental Financial Statement Data [Abstract]
Amortization of deferred policy acquisition costs	$ 1,034,400	$ 917,217	$ 903,154
Other underwriting expenses	398,532	397,266	345,309
Service company expenses	75,231	72,372	78,331
Net foreign currency (gains) losses	(1,884)	2,126	4,213
Other costs and expenses	115,050	107,381	109,831
Total	$ 1,621,329	$ 1,496,362	$ 1,440,838