Supplemental Financial Statement Information (Schedule of Other Operating Cost and Expense, by Component) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Other Income and Expenses [Abstract]
Amortization of deferred policy acquisition costs	$ 1,102,492	$ 1,053,397	$ 991,070
Other underwriting expenses	903,006	843,133	780,058
Service company expenses	127,365	102,726	88,662
Net foreign currency losses (gains)	400	(27)	(10,120)
Other costs and expenses	156,487	158,227	151,014
Total	$ 2,289,750	$ 2,157,456	$ 2,000,684