Reportable Segments - (Net Operating Income) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting Information [Line Items]
Net Operating Income	$ 120,016	$ 120,642	$ 364,930	$ 305,790
Atlanta
Segment Reporting Information [Line Items]
Net Operating Income	43,388	38,926	129,879	115,692
Austin
Segment Reporting Information [Line Items]
Net Operating Income	31,639	29,452	92,161	63,977
Charlotte
Segment Reporting Information [Line Items]
Net Operating Income	14,621	21,692	51,214	55,550
Dallas
Segment Reporting Information [Line Items]
Net Operating Income	3,688	3,416	10,907	4,086
Phoenix
Segment Reporting Information [Line Items]
Net Operating Income	9,205	8,913	27,920	27,694
Tampa
Segment Reporting Information [Line Items]
Net Operating Income	8,230	8,309	24,372	24,869
Other
Segment Reporting Information [Line Items]
Net Operating Income	9,245	9,934	28,477	13,922
Office
Segment Reporting Information [Line Items]
Net Operating Income	119,226	119,974	362,506	303,546
Office | Atlanta
Segment Reporting Information [Line Items]
Net Operating Income	43,360	38,926	129,924	115,692
Office | Austin
Segment Reporting Information [Line Items]
Net Operating Income	31,639	29,452	92,161	63,977
Office | Charlotte
Segment Reporting Information [Line Items]
Net Operating Income	14,621	21,692	51,214	55,550
Office | Dallas
Segment Reporting Information [Line Items]
Net Operating Income	3,688	3,416	10,907	4,086
Office | Phoenix
Segment Reporting Information [Line Items]
Net Operating Income	9,205	8,913	27,920	27,694
Office | Tampa
Segment Reporting Information [Line Items]
Net Operating Income	8,230	8,309	24,372	24,869
Office | Other
Segment Reporting Information [Line Items]
Net Operating Income	8,483	9,266	26,008	11,678
Mixed-Use
Segment Reporting Information [Line Items]
Net Operating Income	790	668	2,424	2,244
Mixed-Use | Atlanta
Segment Reporting Information [Line Items]
Net Operating Income	28	0	(45)	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	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	$ 762	$ 668	$ 2,469	$ 2,244