Reportable Segments Table (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Segment Reporting Information [Line Items]
Fee Income	$ 1,824	$ 1,704	$ 4,023	$ 3,520
Other Revenue from Continuing Operations	129	22	705	143
Net operating property income, including discontinued operations	59,008	60,774	118,521	118,827
Net operating income in joint venture	6,954	5,984	13,600	11,970
General and Administrative Expense	4,691	5,936	13,183	9,533
Interest Expense	(7,334)	(7,869)	(14,748)	(15,546)
Depreciation, Depletion and Amortization	(32,381)	(34,879)	(64,350)	(71,026)
Other Expenses	2,576	343	2,701	783
Reimbursed Expenses	(798)	(717)	(1,668)	(1,828)
Income (Loss) from Equity Method Investments	1,784	1,761	3,618	3,372
Loss on sale from discontinued operations	0	0	0	(551)
Gain on sale of investment properties	(246)	(576)	13,944	530
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	7,765	7,951	30,561	15,155
Houston [Member]
Segment Reporting Information [Line Items]
Net operating property income, including discontinued operations	25,125	25,432	50,443	50,510
Atlanta [Member]
Segment Reporting Information [Line Items]
Net operating property income, including discontinued operations	23,314	24,777	47,526	49,492
Austin [Member]
Segment Reporting Information [Line Items]
Net operating property income, including discontinued operations	5,763	3,914	10,955	6,100
Charlotte [Member]
Segment Reporting Information [Line Items]
Net operating property income, including discontinued operations	4,819	4,011	9,574	7,954
Other [Member]
Segment Reporting Information [Line Items]
Net operating property income, including discontinued operations	(13)	2,640	23	4,771
Mixed-Use [Member]
Segment Reporting Information [Line Items]
Net operating property income, including discontinued operations	1,742	1,499	3,348	2,851
Mixed-Use [Member] | Houston [Member]
Segment Reporting Information [Line Items]
Net operating property income, including discontinued operations	0	0	0	0
Mixed-Use [Member] | Atlanta [Member]
Segment Reporting Information [Line Items]
Net operating property income, including discontinued operations	1,742	1,499	3,348	2,851
Mixed-Use [Member] | Austin [Member]
Segment Reporting Information [Line Items]
Net operating property income, including discontinued operations	0	0	0	0
Mixed-Use [Member] | Charlotte [Member]
Segment Reporting Information [Line Items]
Net operating property income, including discontinued operations	0	0	0	0
Mixed-Use [Member] | Other [Member]
Segment Reporting Information [Line Items]
Net operating property income, including discontinued operations	0	0	0	0
Office Segment [Member]
Segment Reporting Information [Line Items]
Net operating property income, including discontinued operations	57,275	59,269	115,158	115,995
Office Segment [Member] | Houston [Member]
Segment Reporting Information [Line Items]
Net operating property income, including discontinued operations	25,125	25,432	50,443	50,510
Office Segment [Member] | Atlanta [Member]
Segment Reporting Information [Line Items]
Net operating property income, including discontinued operations	21,572	23,272	44,178	46,635
Office Segment [Member] | Austin [Member]
Segment Reporting Information [Line Items]
Net operating property income, including discontinued operations	5,763	3,914	10,955	6,100
Office Segment [Member] | Charlotte [Member]
Segment Reporting Information [Line Items]
Net operating property income, including discontinued operations	4,819	4,011	9,574	7,954
Office Segment [Member] | Other [Member]
Segment Reporting Information [Line Items]
Net operating property income, including discontinued operations	(4)	2,640	8	4,796
Other [Member]
Segment Reporting Information [Line Items]
Net operating property income, including discontinued operations	(9)	6	15	(19)
Other [Member] | Houston [Member]
Segment Reporting Information [Line Items]
Net operating property income, including discontinued operations	0	0	0	0
Other [Member] | Atlanta [Member]
Segment Reporting Information [Line Items]
Net operating property income, including discontinued operations	0	6	0	6
Other [Member] | Austin [Member]
Segment Reporting Information [Line Items]
Net operating property income, including discontinued operations	0	0	0	0
Other [Member] | Charlotte [Member]
Segment Reporting Information [Line Items]
Net operating property income, including discontinued operations	0	0	0	0
Other [Member] | Other [Member]
Segment Reporting Information [Line Items]
Net operating property income, including discontinued operations	$ (9)	$ 0	$ 15	$ (25)