Reportable Segments (Segment Net Operating Income) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Segment Reporting Information [Line Items]
Total Net Operating Income	$ 80,167	$ 59,513
Houston
Segment Reporting Information [Line Items]
Total Net Operating Income		25,318
Atlanta
Segment Reporting Information [Line Items]
Total Net Operating Income	32,244	24,199
Charlotte
Segment Reporting Information [Line Items]
Total Net Operating Income	15,426	4,774
Austin
Segment Reporting Information [Line Items]
Total Net Operating Income	14,187	5,192
Phoenix
Segment Reporting Information [Line Items]
Total Net Operating Income	7,217
Tampa
Segment Reporting Information [Line Items]
Total Net Operating Income	6,837
Orlando
Segment Reporting Information [Line Items]
Total Net Operating Income	3,790
Other
Segment Reporting Information [Line Items]
Total Net Operating Income	466	30
Office
Segment Reporting Information [Line Items]
Total Net Operating Income	77,895	57,912
Office | Houston
Segment Reporting Information [Line Items]
Total Net Operating Income		25,318
Office | Atlanta
Segment Reporting Information [Line Items]
Total Net Operating Income	29,972	22,598
Office | Charlotte
Segment Reporting Information [Line Items]
Total Net Operating Income	15,426	4,774
Office | Austin
Segment Reporting Information [Line Items]
Total Net Operating Income	14,187	5,192
Office | Phoenix
Segment Reporting Information [Line Items]
Total Net Operating Income	7,217
Office | Tampa
Segment Reporting Information [Line Items]
Total Net Operating Income	6,837
Office | Orlando
Segment Reporting Information [Line Items]
Total Net Operating Income	3,790
Office | Other
Segment Reporting Information [Line Items]
Total Net Operating Income	466	30
Mixed-Use
Segment Reporting Information [Line Items]
Total Net Operating Income	2,272	1,601
Mixed-Use | Houston
Segment Reporting Information [Line Items]
Total Net Operating Income		0
Mixed-Use | Atlanta
Segment Reporting Information [Line Items]
Total Net Operating Income	2,272	1,601
Mixed-Use | Charlotte
Segment Reporting Information [Line Items]
Total Net Operating Income	0	0
Mixed-Use | Austin
Segment Reporting Information [Line Items]
Total Net Operating Income	0	0
Mixed-Use | Phoenix
Segment Reporting Information [Line Items]
Total Net Operating Income	0
Mixed-Use | Tampa
Segment Reporting Information [Line Items]
Total Net Operating Income	0
Mixed-Use | Orlando
Segment Reporting Information [Line Items]
Total Net Operating Income	0
Mixed-Use | Other
Segment Reporting Information [Line Items]
Total Net Operating Income	0	0
Other
Segment Reporting Information [Line Items]
Total Net Operating Income	0	0
Other | Houston
Segment Reporting Information [Line Items]
Total Net Operating Income		0
Other | Atlanta
Segment Reporting Information [Line Items]
Total Net Operating Income	0	0
Other | Charlotte
Segment Reporting Information [Line Items]
Total Net Operating Income	0	0
Other | Austin
Segment Reporting Information [Line Items]
Total Net Operating Income	0	0
Other | Phoenix
Segment Reporting Information [Line Items]
Total Net Operating Income	0
Other | Tampa
Segment Reporting Information [Line Items]
Total Net Operating Income	0
Other | Orlando
Segment Reporting Information [Line Items]
Total Net Operating Income	0
Other | Other
Segment Reporting Information [Line Items]
Total Net Operating Income	$ 0	$ 0