Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 324	$ 243
Preferred shares of beneficial interest, liquidation preference value	$ 210,000	$ 350,000
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	8,400,000	14,000,000
Preferred shares of beneficial interest, shares outstanding	8,400,000	14,000,000
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	71,922,904	71,735,129
Common shares of beneficial interest, shares outstanding	71,922,904	71,735,129