Loss And Loss Adjustment Expense Reserves (Activity In The Reserves For Losses And Loss Adjustment Expenses) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Gross reserves at January 1	$ 1,829,412	$ 1,510,613
Less reinsurance recoverables on unpaid losses	(127,634)	(52,794)	$ (180,859)	$ (64,001)
Net reserves at January 1	1,648,553	1,446,612
Incurred losses and loss adjustment expenses related to:
Current year	629,054	589,582
Prior years	1,362	42,652
Total incurred losses and loss adjustment expenses	630,416	632,234
Loss and loss adjustment expense payments related to:
Current year	274,273	254,841
Prior years	344,718	345,826
Total payments	618,991	600,667
Net reserves at March 31	1,659,978	1,478,179
Gross reserves at March 31	$ 1,787,612	$ 1,530,973