Reportable Segments - Segment Revenues (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Segment Reporting Information [Line Items]
Total Revenues	$ 189,550	$ 193,898
Rental property revenues
Segment Reporting Information [Line Items]
Total Revenues	184,807	189,129
Rental property revenues | Office
Segment Reporting Information [Line Items]
Total Revenues	184,807	189,129
Rental property revenues | Mixed-Use
Segment Reporting Information [Line Items]
Total Revenues	0	0
Rental property revenues | Operating segments
Segment Reporting Information [Line Items]
Total Revenues	192,044	198,694
Rental property revenues | Operating segments | Atlanta
Segment Reporting Information [Line Items]
Total Revenues	65,151	65,912
Rental property revenues | Operating segments | Austin
Segment Reporting Information [Line Items]
Total Revenues	58,033	48,747
Rental property revenues | Operating segments | Charlotte
Segment Reporting Information [Line Items]
Total Revenues	21,727	34,537
Rental property revenues | Operating segments | Dallas
Segment Reporting Information [Line Items]
Total Revenues	4,484	4,471
Rental property revenues | Operating segments | Phoenix
Segment Reporting Information [Line Items]
Total Revenues	12,738	13,159
Rental property revenues | Operating segments | Tampa
Segment Reporting Information [Line Items]
Total Revenues	14,571	14,112
Rental property revenues | Operating segments | Other
Segment Reporting Information [Line Items]
Total Revenues	15,340	17,756
Rental property revenues | Operating segments | Office
Segment Reporting Information [Line Items]
Total Revenues	190,440	197,397
Rental property revenues | Operating segments | Office | Atlanta
Segment Reporting Information [Line Items]
Total Revenues	64,792	65,877
Rental property revenues | Operating segments | Office | Austin
Segment Reporting Information [Line Items]
Total Revenues	58,033	48,747
Rental property revenues | Operating segments | Office | Charlotte
Segment Reporting Information [Line Items]
Total Revenues	21,727	34,537
Rental property revenues | Operating segments | Office | Dallas
Segment Reporting Information [Line Items]
Total Revenues	4,484	4,471
Rental property revenues | Operating segments | Office | Phoenix
Segment Reporting Information [Line Items]
Total Revenues	12,738	13,159
Rental property revenues | Operating segments | Office | Tampa
Segment Reporting Information [Line Items]
Total Revenues	14,571	14,112
Rental property revenues | Operating segments | Office | Other
Segment Reporting Information [Line Items]
Total Revenues	14,095	16,494
Rental property revenues | Operating segments | Mixed-Use
Segment Reporting Information [Line Items]
Total Revenues	1,604	1,297
Rental property revenues | Operating segments | Mixed-Use | Atlanta
Segment Reporting Information [Line Items]
Total Revenues	359	35
Rental property revenues | Operating segments | Mixed-Use | Austin
Segment Reporting Information [Line Items]
Total Revenues	0	0
Rental property revenues | Operating segments | Mixed-Use | Charlotte
Segment Reporting Information [Line Items]
Total Revenues	0	0
Rental property revenues | Operating segments | Mixed-Use | Dallas
Segment Reporting Information [Line Items]
Total Revenues	0	0
Rental property revenues | Operating segments | Mixed-Use | Phoenix
Segment Reporting Information [Line Items]
Total Revenues	0	0
Rental property revenues | Operating segments | Mixed-Use | Tampa
Segment Reporting Information [Line Items]
Total Revenues	0	0
Rental property revenues | Operating segments | Mixed-Use | Other
Segment Reporting Information [Line Items]
Total Revenues	1,245	1,262
Rental property revenues | Segment reconciling items
Segment Reporting Information [Line Items]
Total Revenues	(7,237)	(9,565)
Rental property revenues | Segment reconciling items | Office
Segment Reporting Information [Line Items]
Total Revenues	(5,633)	(8,268)
Rental property revenues | Segment reconciling items | Mixed-Use
Segment Reporting Information [Line Items]
Total Revenues	$ (1,604)	$ (1,297)