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
	Mar. 31, 2016	Mar. 31, 2015
Premiums written
Direct	$ 43,176	$ 30,813
Assumed	818,957	612,765
Ceded	(350,458)	(239,543)
Net premiums written	511,675	404,035
Premiums earned
Direct	33,140	22,901
Assumed	456,641	382,603
Ceded	(136,175)	(108,744)
Net premiums earned	353,606	296,760
Claims and claim expenses
Gross claims and claim expenses incurred	161,998	88,995
Claims and claim expenses recovered	(35,393)	(12,142)
Net claims and claim expenses incurred	$ 126,605	$ 76,853