Shareholders' Equity (Schedule Of Preferred Stock Outstanding) (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Class of Stock [Line Items]
Shares Outstanding	39,800	39,800
Amount	$ 995,000	$ 995,000
Series R [Member]
Class of Stock [Line Items]
Issuance Date	Oct. 01, 2010	Oct. 01, 2010
Earliest Potential Redemption Date	Oct. 01, 2015	Oct. 01, 2015
Dividend Rate	6.875%	6.875%
Shares Outstanding	3,000	3,000
Amount	$ 75,000	$ 75,000
Series S [Member]
Class of Stock [Line Items]
Issuance Date	Jan. 01, 2012	Jan. 01, 2012
Earliest Potential Redemption Date	Jan. 01, 2017	Jan. 01, 2017
Dividend Rate	6.45%	6.45%
Shares Outstanding	9,200	9,200
Amount	$ 230,000	$ 230,000
Series T [Member]
Class of Stock [Line Items]
Issuance Date	May 01, 2012	May 01, 2012
Earliest Potential Redemption Date	May 01, 2017	May 01, 2017
Dividend Rate	6.00%	6.00%
Shares Outstanding	14,000	14,000
Amount	$ 350,000	$ 350,000
Series U [Member]
Class of Stock [Line Items]
Issuance Date	Sep. 01, 2012	Sep. 01, 2012
Earliest Potential Redemption Date	Sep. 01, 2017	Sep. 01, 2017
Dividend Rate	5.75%	5.75%
Shares Outstanding	9,200	9,200
Amount	$ 230,000	$ 230,000
Series V [Member]
Class of Stock [Line Items]
Issuance Date	Mar. 01, 2013	Mar. 01, 2013
Earliest Potential Redemption Date	Mar. 01, 2018	Mar. 01, 2018
Dividend Rate	5.70%	5.70%
Shares Outstanding	4,400	4,400
Amount	$ 110,000	$ 110,000