CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $)	Jun. 30, 2013	Dec. 31, 2012
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	199,700,000	199,700,000
Common shares of beneficial interest, shares issued	188,085,568	176,553,600
Common shares of beneficial interest, shares outstanding	188,085,568	176,553,600