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Subsequent Events	12 Months Ended
Subsequent Events	Dec. 31, 2017
Subsequent Events [Abstract]
Subsequent Events [Text Block]	Subsequent Events On February 14, 2018, the Board of Trustees granted awards of an aggregate of 52,609 service condition restricted common shares and 78,918 target performance-based equity to executive officers and employees of the Company. These awards will vest over 3 years. The actual number of common shares to be issued under the performance-based equity awards will be determined in early 2021 and will be based on certain performance criteria stipulated in the agreements for the period January 1, 2018 through December 31, 2020.