Reserves For Losses And LAE (Summary Of Activity In The Reserve For Losses And LAE) (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Reserves For Losses And LAE [Abstract]
Gross reserves at beginning of period	$ 8,331,288	$ 7,940,720
Less reinsurance recoverable	(4,199,791)	(3,875,073)
Net reserves at beginning of period	4,131,497	4,065,647
Incurred related to: Current year	584,656	1,441,962
Incurred related to: Prior years	2,294	(91,682)
Total incurred losses and LAE	586,950	1,350,280
Paid related to: Current year	165,100	400,489
Paid related to: Prior years	493,405	892,207
Total paid losses and LAE	658,505	1,292,696
Foreign exchange/translation adjustment	(6,122)	8,266
Net reserves at end of period	4,053,820	4,131,497
Plus reinsurance recoverable	4,232,779	4,199,791
Gross reserves at end of period	$ 8,286,599	$ 8,331,288