Reportable Segments (Net Operating Income) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting Information [Line Items]
Net Operating Income	$ 120,642	$ 80,858	$ 305,790	$ 241,631
Atlanta
Segment Reporting Information [Line Items]
Net Operating Income	38,926	32,296	115,692	96,639
Austin
Segment Reporting Information [Line Items]
Net Operating Income	29,452	15,180	63,977	45,209
Charlotte
Segment Reporting Information [Line Items]
Net Operating Income	21,692	15,924	55,550	47,197
Dallas
Segment Reporting Information [Line Items]
Net Operating Income	3,416		4,086
Phoenix
Segment Reporting Information [Line Items]
Net Operating Income	8,913	9,265	27,694	27,119
Tampa
Segment Reporting Information [Line Items]
Net Operating Income	8,309	7,446	24,869	22,816
Other
Segment Reporting Information [Line Items]
Net Operating Income	9,934	747	13,922	2,651
Office
Segment Reporting Information [Line Items]
Net Operating Income	119,974	80,421	303,546	240,163
Office | Atlanta
Segment Reporting Information [Line Items]
Net Operating Income	38,926	32,296	115,692	96,639
Office | Austin
Segment Reporting Information [Line Items]
Net Operating Income	29,452	15,180	63,977	45,209
Office | Charlotte
Segment Reporting Information [Line Items]
Net Operating Income	21,692	15,924	55,550	47,197
Office | Dallas
Segment Reporting Information [Line Items]
Net Operating Income	3,416		4,086
Office | Phoenix
Segment Reporting Information [Line Items]
Net Operating Income	8,913	9,265	27,694	27,119
Office | Tampa
Segment Reporting Information [Line Items]
Net Operating Income	8,309	7,446	24,869	22,816
Office | Other
Segment Reporting Information [Line Items]
Net Operating Income	9,266	310	11,678	1,183
Mixed-Use
Segment Reporting Information [Line Items]
Net Operating Income	668	437	2,244	1,468
Mixed-Use | Atlanta
Segment Reporting Information [Line Items]
Net Operating Income	0	0	0	0
Mixed-Use | Austin
Segment Reporting Information [Line Items]
Net Operating Income	0	0	0	0
Mixed-Use | Charlotte
Segment Reporting Information [Line Items]
Net Operating Income	0	0	0	0
Mixed-Use | Dallas
Segment Reporting Information [Line Items]
Net Operating Income	0		0
Mixed-Use | Phoenix
Segment Reporting Information [Line Items]
Net Operating Income	0	0	0	0
Mixed-Use | Tampa
Segment Reporting Information [Line Items]
Net Operating Income	0	0	0	0
Mixed-Use | Other
Segment Reporting Information [Line Items]
Net Operating Income	$ 668	$ 437	$ 2,244	$ 1,468