Shareholders' Equity (Schedule Of Preferred Stock Outstanding) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	9 Months Ended
	Sep. 30, 2011	Dec. 31, 2010
Class of Stock [Line Items]
Shares Outstanding	23,941,826	23,941,826
Amount	$ 598,546	$ 598,546
Series H [Member]
Class of Stock [Line Items]
Preferred Equity Issuance Date	January & October, 2004
Earliest Potential Redemption Date	Jan. 01, 2009
Dividend Rate	7.00%
Shares Outstanding	6,340,776	6,340,776
Amount	158,520	158,520
Series I [Member]
Class of Stock [Line Items]
Preferred Equity Issuance Date	April, 2004
Earliest Potential Redemption Date	Apr. 01, 2009
Dividend Rate	6.875%
Shares Outstanding	2,745,050	2,745,050
Amount	68,626	68,626
Series M [Member]
Class of Stock [Line Items]
Preferred Equity Issuance Date	May, 2005
Earliest Potential Redemption Date	May 01, 2010
Dividend Rate	7.20%
Shares Outstanding	3,182,000	3,182,000
Amount	79,550	79,550
Series O [Member]
Class of Stock [Line Items]
Preferred Equity Issuance Date	June & August, 2006
Earliest Potential Redemption Date	Jun. 01, 2011
Dividend Rate	7.375%
Shares Outstanding	3,384,000	3,384,000
Amount	84,600	84,600
Series P [Member]
Class of Stock [Line Items]
Preferred Equity Issuance Date	January, 2007
Earliest Potential Redemption Date	Jan. 01, 2012
Dividend Rate	6.70%
Shares Outstanding	5,290,000	5,290,000
Amount	132,250	132,250
Series R [Member]
Class of Stock [Line Items]
Preferred Equity Issuance Date	October, 2010
Earliest Potential Redemption Date	Oct. 01, 2015
Dividend Rate	6.875%
Shares Outstanding	3,000,000	3,000,000
Amount	$ 75,000	$ 75,000