Equity And Accumulated Other Comprehensive Loss, Net (Narrative) (Details) (USD $)	3 Months Ended				3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	0 Months Ended	3 Months Ended	12 Months Ended		0 Months Ended		3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012	Dec. 31, 2012	Mar. 31, 2013 Series F Cumulative Convertible Preferred Units [Member]	Dec. 31, 2012 Series F Cumulative Convertible Preferred Units [Member]	Mar. 31, 2013 Series E Cumulative Convertible Preferred Units [Member]	Dec. 31, 2012 Series E Cumulative Convertible Preferred Units [Member]	Feb. 26, 2013 Series D Cumulative Convertible Preferred Units [Member]	Mar. 31, 2013 Series D Cumulative Convertible Preferred Units [Member]	Dec. 31, 2012 Series D Cumulative Convertible Preferred Units [Member]	Feb. 06, 2008 Series D Cumulative Convertible Preferred Units [Member]	Feb. 26, 2013 Common Stock [Member]	Feb. 26, 2013 Common Units [Member]	Mar. 31, 2013 2011 Equity Distribution Agreements [Member]	Jun. 29, 2011 2011 Equity Distribution Agreements [Member]
Equity and Accumulated Other Comprehensive Income (Loss) [Line Items]
Net proceeds from sale of common stock															$ 62,700,000
Conversion of limited partner common units to general partner common units (units)									4,802,180					(3,054,186)
Aggregate offering price of the distribution agreement maximum																400,000,000
Equity distribution agreements at an average price															$ 66.19
Payment of commissions to sales agents															600,000
Gross proceeds from the issuance of common stock			63,346,000
Issuance of common shares															1,000,000
Issuance date										Feb. 06, 2008
Preferred stock, issued					7,300,000	7,300,000	11,500,000	11,500,000		0	4,936,505	13,800,000
Preferred stock, dividend rate					6.625%	6.625%	7.00%	7.00%		5.50%	5.50%
Preferred stock dividend per share amount					$ 1.656		$ 1.750			$ 1.375
Preferred stock, liquidation preference per share/unit					$ 25.00	$ 25.00	$ 25.00	$ 25.00		$ 25.00	$ 25.00
Conversion of preferred stock (shares)									(4,802,180)				3,054,186
Conversion of units									4,802,180					(3,054,186)
Redemption value of OP units	170,600,000			161,500,000
Percentage of operating partnership common units issued	25.00%
Available indebtedness	17,800,000
Acquisition amount	$ 77,900,000	[1]

[1] Purchase prices are all in U.S. dollars. Purchase prices for acquisitions outside the United States are based on the exchange rate at the date of acquisition.