Reinsurance Reinsurance (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Premiums Written
Written premiums, direct	$ 1,601,344	$ 1,553,493	$ 4,852,584	$ 4,699,319
Written premiums, assumed	221,237	225,863	633,200	657,704
Written premiums, ceded	(251,544)	(253,974)	(795,420)	(815,985)
Total net premiums written	1,571,037	1,525,382	4,690,364	4,541,038
Premiums Earned
Earned premiums, direct	1,575,624	1,505,738	4,646,343	4,336,463
Earned premiums, assumed	217,668	216,889	632,362	667,566
Earned premiums, ceded	(261,734)	(261,823)	(782,093)	(761,968)
Net premiums earned	1,531,558	1,460,804	4,496,612	4,242,061
Ceded losses incurred	123,765	128,903	374,084	319,156
Uncollectible reinsurance	1,000		1,000		$ 1,000
Fees and Commissions, Other	$ 45,946	$ 40,821	$ 129,766	$ 116,047