Noncontrolling Interests - Schedule of Fund II Assets (Details)	12 Months Ended
	Dec. 31, 2014
Noncontrolling Interest [Line Items]
Ownership percentage (in percent)	95.50%
Hayden Ferry Lakeside I
Noncontrolling Interest [Line Items]
Location	Phoenix, AZ
Ownership percentage (in percent)	30.00%
Hayden Ferry Lakeside II
Noncontrolling Interest [Line Items]
Location	Phoenix, AZ
Ownership percentage (in percent)	30.00%
Hayden Ferry Lakeside III
Noncontrolling Interest [Line Items]
Location	Phoenix, AZ
Ownership percentage (in percent)	70.00%
Hayden Ferry Lakeside IV and adjacent garage
Noncontrolling Interest [Line Items]
Location	Phoenix, AZ
Ownership percentage (in percent)	30.00%
245 Riverside
Noncontrolling Interest [Line Items]
Location	Jacksonville, FL
Ownership percentage (in percent)	30.00%
3344 Peachtree
Noncontrolling Interest [Line Items]
Location	Atlanta, GA
Ownership percentage (in percent)	33.00%
Two Ravinia
Noncontrolling Interest [Line Items]
Location	Atlanta, GA
Ownership percentage (in percent)	30.00%
Two Liberty Place
Noncontrolling Interest [Line Items]
Location	Philadelphia, PA
Ownership percentage (in percent)	19.00%