Loss And Loss Adjustment Expense Reserves (Activity In The Reserves For Losses And Loss Adjustment Expenses) (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
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	(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	1,957,598	1,781,452
Prior years	10,323	70,398
Total incurred losses and loss adjustment expenses	1,967,921	1,851,850
Loss and loss adjustment expense payments related to:
Current year	1,149,659	1,072,758
Prior years	715,451	695,678
Total payments	1,865,110	1,768,436
Net reserves at September 30	1,751,364	1,530,026
Reinsurance recoverables on unpaid losses	103,847	50,028
Gross reserves at September 30	$ 1,855,211	$ 1,580,054