Reportable Segments (Net Income (Loss) Reconciliation) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Operating Income (Loss)		$ 241,232	$ 215,673	$ 138,080
Reconciliation from Segment Totals to Consolidated
Net operating income from unconsolidated joint ventures		24,335	(25,897)	(27,768)
Net operating income from discontinued operations		14	(1,800)	(6,390)
Fee Income		7,297	12,519	10,891
Other Revenue from Continuing Operations		1,278	4,954	5,430
Other General and Administrative Expense		(17,099)	(19,969)	(22,460)
Reimbursed Expenses		3,430	3,652	5,215
Interest expense		(30,723)	(29,110)	(21,709)
Depreciation and amortization		(135,416)	(140,018)	(76,277)
Other General Expense		(1,299)	(4,654)	(11,154)
Preferred Share Original Issuance Costs	$ 3,500	0	(3,530)	(2,656)
Dividends, Preferred Stock		0	2,955	10,008
INCOME (LOSS) FROM UNCONSOLIDATED JOINT VENTURES		8,302	11,268	67,325
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest		(586)	21,158	14,788
Gain (Loss) on Sale of Properties, Net of Applicable Income Taxes		80,394	12,536	61,288
Net Income (Loss) Attributable to Noncontrolling Interest		(111)	(1,004)	(5,068)
Net Income (Loss) Available to Common Stockholders, Basic		125,518	45,519	109,097
Houston, TX [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)		103,210	100,816	40,199
Atlanta, GA [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)		99,292	79,161	65,722
Austin TX [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)		15,294	6,992	4,029
Charlotte, NC [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)		16,164	6,839	1,208
Other [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)		7,272	18,470	26,922
Other [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)		168	3,395	12,066
Other [Member] | Houston, TX [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)		0	0	0
Other [Member] | Atlanta, GA [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)		0	0	0
Other [Member] | Austin TX [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)		0	0	0
Other [Member] | Charlotte, NC [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)		0	0	0
Other [Member] | Other [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)		168	3,395	12,066
Mixed-Use [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)		5,854	5,727	3,511
Mixed-Use [Member] | Houston, TX [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)		0	0	0
Mixed-Use [Member] | Atlanta, GA [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)		5,854	5,727	3,511
Mixed-Use [Member] | Austin TX [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)		0	0	0
Mixed-Use [Member] | Charlotte, NC [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)		0	0	0
Mixed-Use [Member] | Other [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)		0	0	0
Office Segment [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)		235,210	206,551	122,503
Office Segment [Member] | Houston, TX [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)		103,210	100,816	40,199
Office Segment [Member] | Atlanta, GA [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)		93,438	73,434	62,211
Office Segment [Member] | Austin TX [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)		15,294	6,992	4,029
Office Segment [Member] | Charlotte, NC [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)		16,164	6,839	1,208
Office Segment [Member] | Other [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)		$ 7,104	$ 18,470	$ 14,856