Reportable Segments - (Segment Revenues) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Segment Reporting Information [Line Items]
Total Revenues	$ 179,915	$ 142,020	$ 373,813	$ 274,753
Rental property revenues
Segment Reporting Information [Line Items]
Total Revenues	175,099	134,933	364,228	258,798
Rental property revenues | Office
Segment Reporting Information [Line Items]
Total Revenues	175,099	134,933	364,228	258,798
Rental property revenues | Mixed-Use
Segment Reporting Information [Line Items]
Total Revenues	0	0	0	0
Rental property revenues | Operating segments
Segment Reporting Information [Line Items]
Total Revenues	181,248	150,178	379,943	286,828
Rental property revenues | Operating segments | Atlanta
Segment Reporting Information [Line Items]
Total Revenues	62,586	59,499	128,499	116,969
Rental property revenues | Operating segments | Austin
Segment Reporting Information [Line Items]
Total Revenues	52,455	31,815	101,202	59,907
Rental property revenues | Operating segments | Charlotte
Segment Reporting Information [Line Items]
Total Revenues	20,505	27,110	55,041	50,496
Rental property revenues | Operating segments | Dallas
Segment Reporting Information [Line Items]
Total Revenues	4,487	804	8,958	804
Rental property revenues | Operating segments | Phoenix
Segment Reporting Information [Line Items]
Total Revenues	12,084	12,805	25,243	25,808
Rental property revenues | Operating segments | Tampa
Segment Reporting Information [Line Items]
Total Revenues	12,912	13,471	27,024	26,441
Rental property revenues | Operating segments | Other
Segment Reporting Information [Line Items]
Total Revenues	16,219	4,674	33,976	6,403
Rental property revenues | Operating segments | Office
Segment Reporting Information [Line Items]
Total Revenues	179,943	149,085	377,340	284,551
Rental property revenues | Operating segments | Office | Atlanta
Segment Reporting Information [Line Items]
Total Revenues	62,457	59,499	128,334	116,969
Rental property revenues | Operating segments | Office | Austin
Segment Reporting Information [Line Items]
Total Revenues	52,455	31,815	101,202	59,907
Rental property revenues | Operating segments | Office | Charlotte
Segment Reporting Information [Line Items]
Total Revenues	20,505	27,110	55,041	50,496
Rental property revenues | Operating segments | Office | Dallas
Segment Reporting Information [Line Items]
Total Revenues	4,487	804	8,958	804
Rental property revenues | Operating segments | Office | Phoenix
Segment Reporting Information [Line Items]
Total Revenues	12,084	12,805	25,243	25,808
Rental property revenues | Operating segments | Office | Tampa
Segment Reporting Information [Line Items]
Total Revenues	12,912	13,471	27,024	26,441
Rental property revenues | Operating segments | Office | Other
Segment Reporting Information [Line Items]
Total Revenues	15,043	3,581	31,538	4,126
Rental property revenues | Operating segments | Mixed-Use
Segment Reporting Information [Line Items]
Total Revenues	1,305	1,093	2,603	2,277
Rental property revenues | Operating segments | Mixed-Use | Atlanta
Segment Reporting Information [Line Items]
Total Revenues	129	0	165	0
Rental property revenues | Operating segments | Mixed-Use | Austin
Segment Reporting Information [Line Items]
Total Revenues	0	0	0	0
Rental property revenues | Operating segments | Mixed-Use | Charlotte
Segment Reporting Information [Line Items]
Total Revenues	0	0	0	0
Rental property revenues | Operating segments | Mixed-Use | Dallas
Segment Reporting Information [Line Items]
Total Revenues	0	0	0
Rental property revenues | Operating segments | Mixed-Use | Phoenix
Segment Reporting Information [Line Items]
Total Revenues	0	0	0	0
Rental property revenues | Operating segments | Mixed-Use | Tampa
Segment Reporting Information [Line Items]
Total Revenues	0	0	0	0
Rental property revenues | Operating segments | Mixed-Use | Other
Segment Reporting Information [Line Items]
Total Revenues	1,176	1,093	2,438	2,277
Rental property revenues | Segment reconciling items
Segment Reporting Information [Line Items]
Total Revenues	(6,149)	(15,245)	(15,715)	(28,030)
Rental property revenues | Segment reconciling items | Office
Segment Reporting Information [Line Items]
Total Revenues	(4,844)	(14,152)	(13,112)	(25,753)
Rental property revenues | Segment reconciling items | Mixed-Use
Segment Reporting Information [Line Items]
Total Revenues	$ (1,305)	$ (1,093)	$ (2,603)	$ (2,277)