Reportable Segments (Segment Net Operating Income) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting Information [Line Items]
Total Net Operating Income	$ 80,195	$ 80,115	$ 160,773	$ 160,281
Atlanta
Segment Reporting Information [Line Items]
Total Net Operating Income	32,178	30,071	64,343	62,316
Charlotte
Segment Reporting Information [Line Items]
Total Net Operating Income	15,431	15,202	31,273	30,627
Austin
Segment Reporting Information [Line Items]
Total Net Operating Income	15,088	14,852	30,029	29,039
Phoenix
Segment Reporting Information [Line Items]
Total Net Operating Income	8,880	8,838	17,854	16,056
Tampa
Segment Reporting Information [Line Items]
Total Net Operating Income	7,642	7,451	15,370	14,287
Orlando
Segment Reporting Information [Line Items]
Total Net Operating Income		3,318		7,108
Other
Segment Reporting Information [Line Items]
Total Net Operating Income	976	383	1,904	848
Office
Segment Reporting Information [Line Items]
Total Net Operating Income	79,652	79,262	159,742	157,155
Office | Atlanta
Segment Reporting Information [Line Items]
Total Net Operating Income	32,178	29,218	64,343	59,190
Office | Charlotte
Segment Reporting Information [Line Items]
Total Net Operating Income	15,431	15,202	31,273	30,627
Office | Austin
Segment Reporting Information [Line Items]
Total Net Operating Income	15,088	14,852	30,029	29,039
Office | Phoenix
Segment Reporting Information [Line Items]
Total Net Operating Income	8,880	8,838	17,854	16,056
Office | Tampa
Segment Reporting Information [Line Items]
Total Net Operating Income	7,642	7,451	15,370	14,287
Office | Orlando
Segment Reporting Information [Line Items]
Total Net Operating Income		3,318		7,108
Office | Other
Segment Reporting Information [Line Items]
Total Net Operating Income	433	383	873	848
Mixed-Use
Segment Reporting Information [Line Items]
Total Net Operating Income	543	853	1,031	3,126
Mixed-Use | Atlanta
Segment Reporting Information [Line Items]
Total Net Operating Income	0	853	0	3,126
Mixed-Use | Charlotte
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 | 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 | Orlando
Segment Reporting Information [Line Items]
Total Net Operating Income		0		0
Mixed-Use | Other
Segment Reporting Information [Line Items]
Total Net Operating Income	$ 543	$ 0	$ 1,031	$ 0