Condensed Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2012	Dec. 31, 2011
ASSETS
Allowance for doubtful accounts	$ 9,777	$ 11,301
Preferred Shares of Beneficial Interest - par value, $.03 per share; shares authorized: 10,000
Preferred Shares of Beneficial Interest; par value per share	$ 0.03	$ 0.03
Preferred Shares of Beneficial Interest; shares authorized	10,000,000	10,000,000
Common Shares of Beneficial Interest; par value per share	$ 0.03	$ 0.03
Common Shares of Beneficial Interest; shares authorized	275,000,000	275,000,000
Common Shares of Beneficial Interest; shares issued	121,249,000	120,844,000
Common Shares of Beneficial Interest; shares outstanding	121,249,000	120,844,000
6.75% Series D Preferred Shares [Member]
Preferred Shares of Beneficial Interest - par value, $.03 per share; shares authorized: 10,000
Preferred Shares of Beneficial Interest; shares issued	100,000	100,000
Preferred Shares of Beneficial Interest; shares outstanding	100,000	100,000
Preferred Shares of Beneficial Interest; liquidation preference	75,000	75,000
Preferred Shares of Beneficial Interest; dividend percentage	6.75%	6.75%
6.95% Series E Preferred Shares [Member]
Preferred Shares of Beneficial Interest - par value, $.03 per share; shares authorized: 10,000
Preferred Shares of Beneficial Interest; shares issued	29,000	29,000
Preferred Shares of Beneficial Interest; shares outstanding	29,000	29,000
Preferred Shares of Beneficial Interest; liquidation preference	72,500	72,500
Preferred Shares of Beneficial Interest; dividend percentage	6.95%	6.95%
6.5% Series F Preferred Shares [Member]
Preferred Shares of Beneficial Interest - par value, $.03 per share; shares authorized: 10,000
Preferred Shares of Beneficial Interest; shares issued	140,000	140,000
Preferred Shares of Beneficial Interest; shares outstanding	140,000	140,000
Preferred Shares of Beneficial Interest; liquidation preference	$ 350,000	$ 350,000
Preferred Shares of Beneficial Interest; dividend percentage	6.50%	6.50%