Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 540	$ 494
Preferred shares of beneficial interest, liquidation preference value	$ 250,000	$ 250,000
Preferred shares of beneficial interest, par value (usd per share)	$ 0.01	$ 0.01
Preferred shares of beneficial interest, shares authorized	100,000,000	100,000,000
Preferred shares of beneficial interest, shares issued	10,000,000	10,000,000
Preferred shares of beneficial interest, shares outstanding	10,000,000	10,000,000
Common shares of beneficial interest, par value (usd per share)	$ 0.01	$ 0.01
Common shares of beneficial interest, shares authorized	500,000,000	500,000,000
Common shares of beneficial interest, shares issued	68,816,375	71,922,904
Common shares of beneficial interest, shares outstanding	68,816,375	71,922,904