Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Allowance for doubtful accounts	$ 6,072	$ 7,680
Preferred Shares of Beneficial Interest - par value, $.03 per share; shares authorized: 10,000
Preferred shares of beneficial Interest, par value (in dollars per share)	$ 0.03	$ 0.03
Preferred shares of beneficial Interest, shares authorized (in shares)	10,000,000	10,000,000
Common Shares of Beneficial Interest - par value, $.03 per share; shares authorized: 275,000; shares issued and outstanding: 123,951 in 2015 and 122,489 in 2014
Common shares of beneficial interest, par value (in dollars per share)	$ 0.03	$ 0.03
Common shares of beneficial interest, shares authorized (in shares)	275,000,000	275,000,000
Common shares of beneficial interest, shares issued (in shares)	123,951,000	122,489,000
Common shares of beneficial interest, shares outstanding (in shares)	123,951,000	122,489,000
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 (in shares)	140,000	140,000
Preferred shares of beneficial interest, shares outstanding (in shares)	0	60,000
Preferred shares of beneficial interest, liquidation preference		$ 150,000
Preferred shares of beneficial interest, dividend percentage	6.50%	6.50%