Consolidated Statements of Beneficiaries' Equity (Paranthetical) - $ / shares	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2015
Dividends declared (USD per share)	$ 0.60	$ 0.60	$ 0.60
Cumulative Distributions [Member]
Dividends declared (USD per share)	0.60	0.60	0.60
Noncontrolling Interest [Member]
Dividends declared (USD per share)	$ 0.60	$ 0.60	$ 0.60