Reinsurance Reinsurance (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Premiums Written
Written premiums, direct	$ 1,721,062	$ 1,709,129
Written premiums, assumed	215,145	246,568
Written premiums, ceded	(289,369)	(291,975)
Total net premiums written	1,646,838	1,663,722
Premiums Earned
Earned premiums, direct	1,613,364	1,568,067
Earned premiums, assumed	208,626	218,367
Earned premiums, ceded	(251,948)	(259,099)
Net premiums earned	1,570,042	1,527,335
Ceded losses and loss expenses incurred	35,192	126,929
Uncollectible reinsurance	1,000		$ 1,000
Fees and Commissions, Other	$ 56,550	$ 47,973