Investment in Office Properties - Development Property (Details) - Hayden Ferry Lakeside III - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Real Estate Properties [Line Items]
Direct membership interest (as a percent)	57.142%
Direct and Indirect ownership interest (as a percent)	70.00%
Increase in investment amount	$ 26.1	$ 16.8
Investment amount	42.9
Expected total investment	$ 48.2
Fund II
Real Estate Properties [Line Items]
Direct membership interest (as a percent)	42.858%
Increase in investment amount	$ 37.3	$ 24.0
Investment amount	61.3
Expected total investment	$ 68.8
TRST
Real Estate Properties [Line Items]
Direct and Indirect ownership interest (as a percent)	30.00%