Noncontrolling Interests - Fund II Assets (Details)	9 Months Ended
	Sep. 30, 2015
Hayden Ferry Lakeside I
Noncontrolling Interest [Line Items]
Location	Phoenix, AZ
Company's Ownership %	30.00%
Hayden Ferry Lakeside II
Noncontrolling Interest [Line Items]
Location	Phoenix, AZ
Company's Ownership %	30.00%
Hayden Ferry Lakeside III
Noncontrolling Interest [Line Items]
Location	Phoenix, AZ
Company's Ownership %	70.00%
Hayden Ferry Lakeside IV and adjacent garage
Noncontrolling Interest [Line Items]
Location	Phoenix, AZ
Company's Ownership %	30.00%
3344 Peachtree
Noncontrolling Interest [Line Items]
Location	Atlanta, GA
Company's Ownership %	33.00%
Two Liberty Place
Noncontrolling Interest [Line Items]
Location	Philadelphia, PA
Company's Ownership %	19.00%