Credit Facilities (Summary Of Outstanding Letters Of Credit And Borrowings Of Bermuda Re Letter Of Credit Facility) (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Line of Credit Facility [Line Items]
Commitment	$ 1,100,000
Citibank Bilateral Letter Of Credit Agreement One [Member]
Line of Credit Facility [Line Items]
Commitment	300,000	$ 300,000
In Use	$ 3,672	$ 112
Date of Expiry	Nov. 24, 2015	Aug. 30, 2015
Citibank Bilateral Letter Of Credit Agreement Two [Member]
Line of Credit Facility [Line Items]
In Use	$ 65,013	$ 3,672
Date of Expiry	Dec. 31, 2015	Nov. 24, 2015
Citibank Bilateral Letter Of Credit Agreement Three [Member]
Line of Credit Facility [Line Items]
In Use	$ 2,681	$ 70,922
Date of Expiry	Dec. 31, 2016	Dec. 31, 2015
Citibank Bilateral Letter Of Credit Agreement Four [Member]
Line of Credit Facility [Line Items]
In Use	$ 173	$ 2,014
Date of Expiry	Aug. 30, 2017	Dec. 31, 2016
Citibank Bilateral Letter Of Credit Agreement Five [Member]
Line of Credit Facility [Line Items]
In Use	$ 119,002	$ 149,353
Date of Expiry	Sep. 30, 2019	Dec. 30, 2018
Citibank Bilateral Agreement [Member]
Line of Credit Facility [Line Items]
Commitment	$ 300,000	$ 300,000
In Use	$ 190,541	$ 226,073