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, 2012	Dec. 31, 2011	Dec. 31, 2010
Supplemental Financial Statement Data [Abstract]
Amortization of deferred policy acquisition costs	$ 917,583	$ 785,118	$ 708,577
Other underwriting expenses	675,163	653,011	610,301
Service company expenses	84,986	75,231	72,372
Net foreign currency (gains) losses	(6,092)	(1,884)	2,126
Other costs and expenses	127,983	115,050	107,381
Total	$ 1,799,623	$ 1,626,526	$ 1,500,757