Reinsurance (Effect Of Reinsurance And Retrocessional Activity On Premiums Written And Earned And On Net Claims And Claim Expenses) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Premiums written
Direct	$ 53,488	$ 31,781	$ 154,205	$ 96,934
Assumed	376,736	337,861	1,897,280	1,578,283
Ceded	(146,002)	(102,822)	(735,672)	(495,685)
Net premiums written	284,222	266,820	1,315,813	1,179,532
Premiums earned
Direct	43,097	26,040	114,173	70,547
Assumed	471,097	456,957	1,392,278	1,307,932
Ceded	(167,673)	(120,609)	(454,922)	(339,503)
Net premiums earned	346,521	362,388	1,051,529	1,038,976
Claims and claim expenses
Gross claims and claim expenses incurred	153,846	121,744	540,696	433,558
Claims and claim expenses recovered	(41,271)	(21,716)	(133,766)	(87,333)
Net claims and claim expenses incurred	$ 112,575	$ 100,028	$ 406,930	$ 346,225