Consolidated Statements of Beneficiaries' Equity (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Distributions declared per Common Share	$ 0.66	$ 0.63	$ 0.60
Cumulative Distributions [Member]
Distributions declared per Common Share	0.66	0.63	0.60
Noncontrolling Interest [Member]
Distributions declared per Common Share	$ 0.66	$ 0.63	$ 0.60