Reinsurance Reinsurance (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Premiums Written
Written premiums, direct	$ 1,603,899	$ 1,580,639	$ 3,251,240	$ 3,145,827
Written premiums, assumed	207,499	191,762	411,963	431,841
Written premiums, ceded	(267,473)	(282,625)	(543,876)	(562,012)
Total net premiums written	1,543,925	1,489,776	3,119,327	3,015,656
Premiums Earned
Earned premiums, direct	1,545,983	1,449,152	3,070,719	2,830,724
Earned premiums, assumed	211,352	224,916	414,694	450,678
Earned premiums, ceded	(264,294)	(256,423)	(520,359)	(500,145)
Net premiums earned	1,493,041	1,417,645	2,965,054	2,781,257
Ceded losses incurred	131,928	89,569	250,319	190,253
Uncollectible reinsurance	1,000		1,000		$ 1,000
Fees and Commissions, Other	$ 40,169	$ 38,055	$ 83,820	$ 75,226