CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2015	Dec. 31, 2014
CONDENSED CONSOLIDATED BALANCE SHEETS
Common shares of beneficial interest, par value (in dollars per share)	$ 0.01	$ 0.01
Common shares of beneficial interest, shares authorized	100,000,000	100,000,000
Common shares of beneficial interest, shares issued	71,126,308	70,349,227
Common shares of beneficial interest, shares outstanding	71,126,308	70,349,227