Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 6,888	$ 6,072
Common Shares of Beneficial Interest - par value, $.03 per share; shares authorized: 275,000; shares issued and outstanding: 124,871 in 2016 and 123,951 in 2015
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	124,871,000	123,951,000
Common Shares of Beneficial Interest - shares outstanding	124,871,000	123,951,000