Reinsurance Reinsurance (Details) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Premiums Written
Written premiums, direct	$ 1,565,188,000	$ 1,400,412,000
Written premiums, assumed	240,079,000	231,209,000
Written premiums, ceded	279,387,000	254,655,000
Total net premiums written	1,525,880,000	1,376,966,000
Premiums Earned
Earned premiums, direct	1,381,572,000	1,240,562,000
Earned premiums, assumed	225,762,000	214,016,000
Earned premiums, ceded	(243,722,000)	(222,459,000)
Net premiums earned	1,363,612,000	1,232,119,000
Ceded losses incurred	100,684,000	110,551,000
Uncollectible reinsurance	$ 1,000,000		$ 1,000,000