Reinsurance (Reinsurance Financial Information) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Reinsurance Disclosures [Abstract]
Written premiums, Direct	$ 5,626,172	$ 4,964,069	$ 4,370,092
Written premiums, Assumed	884,919	815,810	707,221
Written premiums, Ceded	(1,010,918)	(881,340)	(719,945)
Total net premiums written	5,500,173	4,898,539	4,357,368
Earned premiums, Direct	5,328,955	4,723,882	4,164,277
Earned premiums, Assumed	857,119	770,981	669,593
Earned premiums, Ceded	(959,537)	(821,347)	(673,003)
Net premiums earned	5,226,537	4,673,516	4,160,867
Ceded losses incurred	556,108	528,018	458,249
Uncollectible reinsurance	$ 1,385	$ 1,680	$ 3,169