Reportable Segments (Segment Net Operating Income) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Total Net Operating Income	$ 260,282	$ 241,232	$ 215,673
Houston
Segment Reporting Information [Line Items]
Total Net Operating Income	78,590	103,210	100,816
Atlanta
Segment Reporting Information [Line Items]
Total Net Operating Income	105,443	99,292	79,161
Austin
Segment Reporting Information [Line Items]
Total Net Operating Income	29,865	15,294	6,992
Charlotte
Segment Reporting Information [Line Items]
Total Net Operating Income	28,418	16,164	6,839
Orlando
Segment Reporting Information [Line Items]
Total Net Operating Income	3,265
Tampa
Segment Reporting Information [Line Items]
Total Net Operating Income	7,130
Tempe
Segment Reporting Information [Line Items]
Total Net Operating Income	6,067
Other
Segment Reporting Information [Line Items]
Total Net Operating Income	1,504	7,272	21,865
Office
Segment Reporting Information [Line Items]
Total Net Operating Income	252,871	235,210	206,551
Office | Houston
Segment Reporting Information [Line Items]
Total Net Operating Income	78,590	103,210	100,816
Office | Atlanta
Segment Reporting Information [Line Items]
Total Net Operating Income	98,032	93,438	73,434
Office | Austin
Segment Reporting Information [Line Items]
Total Net Operating Income	29,865	15,294	6,992
Office | Charlotte
Segment Reporting Information [Line Items]
Total Net Operating Income	28,418	16,164	6,839
Office | Orlando
Segment Reporting Information [Line Items]
Total Net Operating Income	3,265
Office | Tampa
Segment Reporting Information [Line Items]
Total Net Operating Income	7,130
Office | Tempe
Segment Reporting Information [Line Items]
Total Net Operating Income	6,067
Office | Other
Segment Reporting Information [Line Items]
Total Net Operating Income	1,504	7,104	18,470
Mixed-Use
Segment Reporting Information [Line Items]
Total Net Operating Income	7,411	5,854	5,727
Mixed-Use | Houston
Segment Reporting Information [Line Items]
Total Net Operating Income	0	0	0
Mixed-Use | Atlanta
Segment Reporting Information [Line Items]
Total Net Operating Income	7,411	5,854	5,727
Mixed-Use | Austin
Segment Reporting Information [Line Items]
Total Net Operating Income	0	0	0
Mixed-Use | Charlotte
Segment Reporting Information [Line Items]
Total Net Operating Income	0	0	0
Mixed-Use | Orlando
Segment Reporting Information [Line Items]
Total Net Operating Income	0
Mixed-Use | Tampa
Segment Reporting Information [Line Items]
Total Net Operating Income	0
Mixed-Use | Tempe
Segment Reporting Information [Line Items]
Total Net Operating Income	0
Mixed-Use | Other
Segment Reporting Information [Line Items]
Total Net Operating Income	0	0	0
Other
Segment Reporting Information [Line Items]
Total Net Operating Income	0	168	3,395
Other | Houston
Segment Reporting Information [Line Items]
Total Net Operating Income	0	0	0
Other | Atlanta
Segment Reporting Information [Line Items]
Total Net Operating Income	0	0	0
Other | Austin
Segment Reporting Information [Line Items]
Total Net Operating Income	0	0	0
Other | Charlotte
Segment Reporting Information [Line Items]
Total Net Operating Income	0	0	0
Other | Orlando
Segment Reporting Information [Line Items]
Total Net Operating Income	0
Other | Tampa
Segment Reporting Information [Line Items]
Total Net Operating Income	0
Other | Tempe
Segment Reporting Information [Line Items]
Total Net Operating Income	0
Other | Other
Segment Reporting Information [Line Items]
Total Net Operating Income	$ 0	$ 168	$ 3,395