Reportable Segments (Net Operating Income) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Segment Reporting Information [Line Items]
Total Net Operating Income	$ 97,417	$ 80,195	$ 185,148	$ 160,773
Atlanta
Segment Reporting Information [Line Items]
Total Net Operating Income	39,368	32,178	76,766	64,343
Austin
Segment Reporting Information [Line Items]
Total Net Operating Income	18,577	15,431	34,525	31,273
Charlotte
Segment Reporting Information [Line Items]
Total Net Operating Income	18,050	15,088	33,859	30,029
Dallas
Segment Reporting Information [Line Items]
Total Net Operating Income	669		670
Phoenix
Segment Reporting Information [Line Items]
Total Net Operating Income	9,290	8,880	18,781	17,854
Tampa
Segment Reporting Information [Line Items]
Total Net Operating Income	8,573	7,642	16,560	15,370
Other
Segment Reporting Information [Line Items]
Total Net Operating Income	2,890	976	3,987	1,904
Office
Segment Reporting Information [Line Items]
Total Net Operating Income	96,709	79,652	183,572	159,742
Office | Atlanta
Segment Reporting Information [Line Items]
Total Net Operating Income	39,368	32,178	76,766	64,343
Office | Austin
Segment Reporting Information [Line Items]
Total Net Operating Income	18,577	15,431	34,525	31,273
Office | Charlotte
Segment Reporting Information [Line Items]
Total Net Operating Income	18,050	15,088	33,859	30,029
Office | Dallas
Segment Reporting Information [Line Items]
Total Net Operating Income	669		670
Office | Phoenix
Segment Reporting Information [Line Items]
Total Net Operating Income	9,290	8,880	18,781	17,854
Office | Tampa
Segment Reporting Information [Line Items]
Total Net Operating Income	8,573	7,642	16,560	15,370
Office | Other
Segment Reporting Information [Line Items]
Total Net Operating Income	2,182	433	2,411	873
Mixed-Use
Segment Reporting Information [Line Items]
Total Net Operating Income	708	543	1,576	1,031
Mixed-Use | Atlanta
Segment Reporting Information [Line Items]
Total Net Operating Income	0	0	0	0
Mixed-Use | Austin
Segment Reporting Information [Line Items]
Total Net Operating Income	0	0	0	0
Mixed-Use | Charlotte
Segment Reporting Information [Line Items]
Total Net Operating Income	0	0	0	0
Mixed-Use | Dallas
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	0	0
Mixed-Use | Tampa
Segment Reporting Information [Line Items]
Total Net Operating Income	0	0	0	0
Mixed-Use | Other
Segment Reporting Information [Line Items]
Total Net Operating Income	$ 708	$ 543	$ 1,576	$ 1,031