Credit Facilities (Summary Of Outstanding Letters Of Credit And/Or Borrowings Of Group Credit Facility) (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Line of Credit Facility [Line Items]
Commitment	$ 1,100,000
Wells Fargo Bank Group Credit Facility Tranche One [Member]
Line of Credit Facility [Line Items]
Commitment	200,000	$ 200,000
Wells Fargo Bank Group Credit Facility Tranche Two Issuance One [Member]
Line of Credit Facility [Line Items]
Commitment	600,000	600,000
In Use	$ 450,100	$ 444,012
Date of Expiry	Dec. 31, 2015	Dec. 31, 2015
Wells Fargo Bank Group Credit Facility [Member]
Line of Credit Facility [Line Items]
Commitment	$ 800,000	$ 800,000
In Use	$ 450,100	$ 444,012