Reportable Segments (Net Operating Income) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Segment Reporting Information [Line Items]
Total Net Operating Income	$ 87,731	$ 80,578
Atlanta
Segment Reporting Information [Line Items]
Total Net Operating Income	37,399	32,165
Austin
Segment Reporting Information [Line Items]
Total Net Operating Income	15,948	14,941
Charlotte
Segment Reporting Information [Line Items]
Total Net Operating Income	15,808	15,842
Phoenix
Segment Reporting Information [Line Items]
Total Net Operating Income	9,491	8,974
Tampa
Segment Reporting Information [Line Items]
Total Net Operating Income	7,988	7,728
Other
Segment Reporting Information [Line Items]
Total Net Operating Income	1,097	928
Office
Segment Reporting Information [Line Items]
Total Net Operating Income	86,864	80,090
Office | Atlanta
Segment Reporting Information [Line Items]
Total Net Operating Income	37,399	32,165
Office | Austin
Segment Reporting Information [Line Items]
Total Net Operating Income	15,948	14,941
Office | Charlotte
Segment Reporting Information [Line Items]
Total Net Operating Income	15,808	15,842
Office | Phoenix
Segment Reporting Information [Line Items]
Total Net Operating Income	9,491	8,974
Office | Tampa
Segment Reporting Information [Line Items]
Total Net Operating Income	7,988	7,728
Office | Other
Segment Reporting Information [Line Items]
Total Net Operating Income	230	440
Mixed-Use
Segment Reporting Information [Line Items]
Total Net Operating Income	867	488
Mixed-Use | Atlanta
Segment Reporting Information [Line Items]
Total Net Operating Income	0	0
Mixed-Use | Austin
Segment Reporting Information [Line Items]
Total Net Operating Income	0	0
Mixed-Use | Charlotte
Segment Reporting Information [Line Items]
Total Net Operating Income	0	0
Mixed-Use | Phoenix
Segment Reporting Information [Line Items]
Total Net Operating Income	0	0
Mixed-Use | Tampa
Segment Reporting Information [Line Items]
Total Net Operating Income	0	0
Mixed-Use | Other
Segment Reporting Information [Line Items]
Total Net Operating Income	$ 867	$ 488