Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Per Share data, unless otherwise specified			12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 6.75% Series D Preferred Shares [Member]	Dec. 31, 2011 6.75% Series D Preferred Shares [Member]	Dec. 31, 2012 6.95% Series E Preferred Shares [Member]	Dec. 31, 2011 6.95% Series E Preferred Shares [Member]	Dec. 31, 2012 6.5% Series F Preferred Shares [Member]	Dec. 31, 2011 6.5% Series F Preferred Shares [Member]
ASSETS
Allowance for doubtful accounts	$ 12,127	$ 11,301
Preferred Shares of Beneficial Interest - par value, $.03 per share; shares authorized: 10,000
Preferred shares of beneficial Interest; par value	$ 0.03	$ 0.03
Preferred shares of beneficial Interest; shares authorized	10,000	10,000
Preferred shares of beneficial interest; shares issued			100	100	29	29	140	140
Preferred shares of beneficial interest; shares outstanding			100	100	0	29	140	140
Preferred shares of beneficial interest; liquidation preference			$ 75,000	$ 75,000	$ 0	$ 72,500	$ 350,000	$ 350,000
Preferred shares of beneficial interest; dividend percentage			6.75%	6.75%	6.95%	6.95%	6.50%	6.50%
Common Shares of Beneficial Interest—par value, $.03 per share; shares authorized:275,000; shares issued and outstanding: 121,505 in 2012 and 120,844 in 2011
Common shares of beneficial interest; par value	$ 0.03	$ 0.03
Common shares of beneficial interest; shares authorized	275,000	275,000
Common shares of beneficial interest; shares issued	121,505	120,844
Common shares of beneficial interest; shares outstanding	121,505	120,844