Reinsurance (Effect Of Reinsurance And Retrocessional Reinsurance On Premiums Written And Earned) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Reinsurance Disclosures [Abstract]
Direct premiums written	$ 957,244	$ 951,885	$ 1,836,332	$ 1,753,465
Direct premiums earned	865,943	875,376	1,733,387	1,719,946
Assumed premiums written	320,405	313,901	833,980	764,794
Assumed premiums earned	295,868	304,324	585,931	617,159
Ceded premiums written	(227,103)	(231,442)	(437,806)	(448,485)
Ceded premiums earned	(210,952)	(222,143)	(410,773)	(435,898)
Net premiums written	1,050,546	1,034,344	2,232,506	2,069,774
Net premiums earned	$ 950,859	$ 957,557	$ 1,908,545	$ 1,901,207