Quarterly report pursuant to Section 13 or 15(d)

CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) (Parenthetical)

v3.8.0.1
CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) (Parenthetical) - $ / shares
Mar. 31, 2018
Dec. 31, 2017
Statement of Financial Position [Abstract]    
Preferred shares of beneficial interest, par value (in dollars per share) $ 0.01 $ 0.01
Preferred shares of beneficial interest, authorized (in shares) 50,000,000 50,000,000
Preferred shares of beneficial interest, issued (in shares) 6,900,000 6,900,000
Preferred shares of beneficial interest, outstanding (in shares) 6,900,000 6,900,000
Common shares of beneficial interest, par value (in dollars per share) $ 0.01 $ 0.01
Common shares of beneficial interest, authorized (in shares) 250,000,000 250,000,000
Common shares of beneficial interest, issued (in shares) 50,438,731 50,284,934
Common shares of beneficial interest, outstanding (in shares) 50,438,731 50,284,934