Losses And Loss Adjustment Expense Reserves (Activity In The Reserves For Losses And Loss Adjustment Expenses) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Gross reserves at January 1	$ 1,290,248	$ 1,146,688	$ 1,091,797
Reinsurance recoverables on unpaid losses	64,001	13,161	14,253	$ 14,192
Net reserves at January 1	1,277,087	1,132,435	1,077,605
Acquisition of WAIC reserves	0	0	18,677
Incurred losses and loss adjustment expense related to:
Current year	2,390,453	2,269,769	2,132,837
Prior year claims and claim adjustment expense	54,431	85,369	12,658
Total incurred losses and loss adjustment expenses	2,444,884	2,355,138	2,145,495
Loss and loss adjustment expense payments related to:
Current year	1,550,789	1,508,362	1,455,245
Prior years	724,570	702,124	654,097
Total payments	2,275,359	2,210,486	2,109,342
Net reserves at year-end	1,446,612	1,277,087	1,132,435
Gross reserves at year-end	$ 1,510,613	$ 1,290,248	$ 1,146,688