Reportable Segments (Segment Net Operating Income) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Total Net Operating Income	$ 80,858	$ 75,815	$ 241,631	$ 236,097
Atlanta
Segment Reporting Information [Line Items]
Total Net Operating Income	32,296	25,247	96,639	87,562
Charlotte
Segment Reporting Information [Line Items]
Total Net Operating Income	15,924	15,074	47,197	46,117
Austin
Segment Reporting Information [Line Items]
Total Net Operating Income	15,180	15,489	45,209	44,113
Phoenix
Segment Reporting Information [Line Items]
Total Net Operating Income	9,265	8,667	27,119	24,722
Tampa
Segment Reporting Information [Line Items]
Total Net Operating Income	7,446	7,412	22,816	21,700
Orlando
Segment Reporting Information [Line Items]
Total Net Operating Income		3,356		10,464
Other
Segment Reporting Information [Line Items]
Total Net Operating Income	747	570	2,651	1,419
Office
Segment Reporting Information [Line Items]
Total Net Operating Income	80,421	75,770	240,163	232,927
Office | Atlanta
Segment Reporting Information [Line Items]
Total Net Operating Income	32,296	25,247	96,639	84,437
Office | Charlotte
Segment Reporting Information [Line Items]
Total Net Operating Income	15,924	15,074	47,197	46,117
Office | Austin
Segment Reporting Information [Line Items]
Total Net Operating Income	15,180	15,489	45,209	44,113
Office | Phoenix
Segment Reporting Information [Line Items]
Total Net Operating Income	9,265	8,667	27,119	24,722
Office | Tampa
Segment Reporting Information [Line Items]
Total Net Operating Income	7,446	7,412	22,816	21,700
Office | Orlando
Segment Reporting Information [Line Items]
Total Net Operating Income		3,356		10,464
Office | Other
Segment Reporting Information [Line Items]
Total Net Operating Income	310	525	1,183	1,374
Mixed-Use
Segment Reporting Information [Line Items]
Total Net Operating Income	437	45	1,468	3,170
Mixed-Use | Atlanta
Segment Reporting Information [Line Items]
Total Net Operating Income	0	0	0	3,125
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	$ 437	$ 45	$ 1,468	$ 45