Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 31, 2011		Sep. 30, 2011		Jun. 30, 2011		Mar. 31, 2011		Dec. 31, 2010		Sep. 30, 2010		Jun. 30, 2010		Mar. 31, 2010		Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Segment Reporting [Abstract]
Limit of consolidated revenue generated by any single customer																	10.00%
Segment Reporting Information [Line Items]
Rental and other revenues	$ 128,730	[1]	$ 122,086	[1]	$ 117,057	[1]	$ 114,979	[1]	$ 117,330	[1]	$ 115,528	[1]	$ 113,765	[1]	$ 114,503	[1]	$ 482,852		$ 461,126		$ 448,018
Total Net Operating Income																	306,704		297,488		285,993
Reconciliation to income from continuing operations before disposition of property, condominiums and investment in unconsolidated affiliates and equity in earnings of unconsolidated affiliates:
Depreciation and amortization																	(143,019)		(135,414)		(129,652)
Impairment of assets held for use																	(2,429)		0		(2,554)
General and administrative expense																	(35,727)		(32,948)		(36,682)
Interest expense																	(95,999)		(93,372)		(86,805)
Interest and other income																	7,363		5,655		9,549
Income from continuing operations before disposition of property, condominiums and investment in unconsolidated affiliates and equity in earnings of unconsolidated affiliates																	36,893		41,409		39,849
Total Assets	3,180,992								2,871,835								3,180,992		2,871,835		2,887,101
Office Total Segment [Member]
Segment Reporting Information [Line Items]
Rental and other revenues																	420,420	[2]	398,709	[2]	388,242	[2]
Total Net Operating Income																	266,836	[2]	257,442	[2]	246,413	[2]
Reconciliation to income from continuing operations before disposition of property, condominiums and investment in unconsolidated affiliates and equity in earnings of unconsolidated affiliates:
Total Assets	2,611,596								2,302,267								2,611,596		2,302,267		2,299,559
Office Atlanta, GA [Member]
Segment Reporting Information [Line Items]
Rental and other revenues																	52,999		48,051		48,704
Total Net Operating Income																	33,744		30,370		30,759
Reconciliation to income from continuing operations before disposition of property, condominiums and investment in unconsolidated affiliates and equity in earnings of unconsolidated affiliates:
Total Assets	359,225								268,772								359,225		268,772		275,464
Office Baltimore, MD [Member]
Reconciliation to income from continuing operations before disposition of property, condominiums and investment in unconsolidated affiliates and equity in earnings of unconsolidated affiliates:
Total Assets	1,789								1,787								1,789		1,787		1,787
Office Greenville, SC [Member]
Segment Reporting Information [Line Items]
Rental and other revenues																	14,079		13,616		14,010
Total Net Operating Income																	8,335		8,145		8,707
Reconciliation to income from continuing operations before disposition of property, condominiums and investment in unconsolidated affiliates and equity in earnings of unconsolidated affiliates:
Total Assets	69,669								73,931								69,669		73,931		78,567
Office Kansas City, MO [Member]
Segment Reporting Information [Line Items]
Rental and other revenues																	14,391		14,822		14,839
Total Net Operating Income																	8,403		8,882		9,072
Reconciliation to income from continuing operations before disposition of property, condominiums and investment in unconsolidated affiliates and equity in earnings of unconsolidated affiliates:
Total Assets	86,028								84,197								86,028		84,197		85,681
Office Memphis, TN [Member]
Segment Reporting Information [Line Items]
Rental and other revenues																	40,324		34,982		30,642
Total Net Operating Income																	23,075		20,828		17,700
Reconciliation to income from continuing operations before disposition of property, condominiums and investment in unconsolidated affiliates and equity in earnings of unconsolidated affiliates:
Total Assets	265,259								270,091								265,259		270,091		220,722
Office Nashville, TN [Member]
Segment Reporting Information [Line Items]
Rental and other revenues																	60,857		59,151		60,551
Total Net Operating Income																	40,341		39,281		39,072
Reconciliation to income from continuing operations before disposition of property, condominiums and investment in unconsolidated affiliates and equity in earnings of unconsolidated affiliates:
Total Assets	325,272								326,855								325,272		326,855		338,124
Office Orlando, FL [Member]
Segment Reporting Information [Line Items]
Rental and other revenues																	10,235		11,615		11,809
Total Net Operating Income																	5,188		6,259		6,268
Reconciliation to income from continuing operations before disposition of property, condominiums and investment in unconsolidated affiliates and equity in earnings of unconsolidated affiliates:
Total Assets	46,547								47,042								46,547		47,042		48,821
Office Piedmont Triad, NC [Member]
Segment Reporting Information [Line Items]
Rental and other revenues																	20,650		21,155		21,255
Total Net Operating Income																	13,045		13,894		13,935
Reconciliation to income from continuing operations before disposition of property, condominiums and investment in unconsolidated affiliates and equity in earnings of unconsolidated affiliates:
Total Assets	115,096								126,680								115,096		126,680		141,971
Office Pittsburgh, PA [Member]
Segment Reporting Information [Line Items]
Rental and other revenues																	10,971		0		0
Total Net Operating Income																	5,456		0		0
Reconciliation to income from continuing operations before disposition of property, condominiums and investment in unconsolidated affiliates and equity in earnings of unconsolidated affiliates:
Total Assets	227,965								0								227,965		0		0
Office Raleigh, NC [Member]
Segment Reporting Information [Line Items]
Rental and other revenues																	78,513		75,604		72,521
Total Net Operating Income																	54,590		52,254		48,784
Reconciliation to income from continuing operations before disposition of property, condominiums and investment in unconsolidated affiliates and equity in earnings of unconsolidated affiliates:
Total Assets	465,813								457,945								465,813		457,945		464,729
Office Richmond, VA [Member]
Segment Reporting Information [Line Items]
Rental and other revenues																	47,536		47,191		46,617
Total Net Operating Income																	31,290		32,049		32,027
Reconciliation to income from continuing operations before disposition of property, condominiums and investment in unconsolidated affiliates and equity in earnings of unconsolidated affiliates:
Total Assets	254,364								249,036								254,364		249,036		249,881
Office Tampa, FL [Member]
Segment Reporting Information [Line Items]
Rental and other revenues																	69,865		72,522		67,294
Total Net Operating Income																	43,369		45,480		40,089
Reconciliation to income from continuing operations before disposition of property, condominiums and investment in unconsolidated affiliates and equity in earnings of unconsolidated affiliates:
Total Assets	394,569								395,931								394,569		395,931		393,812
Industrial Total Segment [Member]
Segment Reporting Information [Line Items]
Rental and other revenues																	27,740	[2]	27,535	[2]	28,389	[2]
Total Net Operating Income																	19,854	[2]	19,713	[2]	21,350	[2]
Reconciliation to income from continuing operations before disposition of property, condominiums and investment in unconsolidated affiliates and equity in earnings of unconsolidated affiliates:
Total Assets	211,721								215,179								211,721		215,179		228,870
Industrial Atlanta, GA [Member]
Segment Reporting Information [Line Items]
Rental and other revenues																	15,911		15,159		15,611
Total Net Operating Income																	11,199		10,671		11,608
Reconciliation to income from continuing operations before disposition of property, condominiums and investment in unconsolidated affiliates and equity in earnings of unconsolidated affiliates:
Total Assets	133,640								135,858								133,640		135,858		136,570
Industrial Piedmont Triad, NC [Member]
Segment Reporting Information [Line Items]
Rental and other revenues																	11,829		12,376		12,778
Total Net Operating Income																	8,655		9,042		9,742
Reconciliation to income from continuing operations before disposition of property, condominiums and investment in unconsolidated affiliates and equity in earnings of unconsolidated affiliates:
Total Assets	78,081								79,321								78,081		79,321		92,300
Total Retail Segment [Member]
Segment Reporting Information [Line Items]
Rental and other revenues																	34,423	[2]	33,662	[2]	30,302	[2]
Total Net Operating Income																	20,190	[2]	19,953	[2]	18,176	[2]
Reconciliation to income from continuing operations before disposition of property, condominiums and investment in unconsolidated affiliates and equity in earnings of unconsolidated affiliates:
Total Assets	177,888								177,592								177,888		177,592		183,931
Retail Atlanta, GA [Member]
Segment Reporting Information [Line Items]
Total Net Operating Income																	(22)	[3]	(21)	[3]	(22)	[3]
Reconciliation to income from continuing operations before disposition of property, condominiums and investment in unconsolidated affiliates and equity in earnings of unconsolidated affiliates:
Total Assets	504								306								504		306		1,044
Retail Kansas City, MO [Member]
Segment Reporting Information [Line Items]
Rental and other revenues																	34,277		33,527		29,997
Total Net Operating Income																	20,163		19,937		18,177
Reconciliation to income from continuing operations before disposition of property, condominiums and investment in unconsolidated affiliates and equity in earnings of unconsolidated affiliates:
Total Assets	170,717								172,116								170,717		172,116		175,757
Retail Piedmont Triad, NC [Member]
Segment Reporting Information [Line Items]
Rental and other revenues																	0		0		185
Total Net Operating Income																	0		0		12
Reconciliation to income from continuing operations before disposition of property, condominiums and investment in unconsolidated affiliates and equity in earnings of unconsolidated affiliates:
Total Assets	0								0								0		0		1,082
Retail Raleigh, NC [Member]
Segment Reporting Information [Line Items]
Rental and other revenues																	146		135		120
Total Net Operating Income																	49		37		9
Reconciliation to income from continuing operations before disposition of property, condominiums and investment in unconsolidated affiliates and equity in earnings of unconsolidated affiliates:
Total Assets	6,667								5,170								6,667		5,170		6,048
Total Residential Segment [Member]
Segment Reporting Information [Line Items]
Rental and other revenues																	269	[2]	1,220	[2]	1,085	[2]
Total Net Operating Income																	(176)	[2]	380	[2]	54	[2]
Reconciliation to income from continuing operations before disposition of property, condominiums and investment in unconsolidated affiliates and equity in earnings of unconsolidated affiliates:
Total Assets	12,573								17,597								12,573		17,597		24,567
Residential Kansas City, MO [Member]
Segment Reporting Information [Line Items]
Rental and other revenues																	269		1,220		1,085
Total Net Operating Income																	19		742		581
Reconciliation to income from continuing operations before disposition of property, condominiums and investment in unconsolidated affiliates and equity in earnings of unconsolidated affiliates:
Total Assets	5,707								5,925								5,707		5,925		6,129
Residential Orlando, FL [Member]
Reconciliation to income from continuing operations before disposition of property, condominiums and investment in unconsolidated affiliates and equity in earnings of unconsolidated affiliates:
Total Assets	2,098								2,098								2,098		2,098		2,147
Residential Raleigh, NC [Member]
Segment Reporting Information [Line Items]
Total Net Operating Income																	(195)	[3]	(362)	[3]	(527)	[3]
Reconciliation to income from continuing operations before disposition of property, condominiums and investment in unconsolidated affiliates and equity in earnings of unconsolidated affiliates:
Total Assets	4,768								9,574								4,768		9,574		16,291
Total Corporate Segment [Member]
Reconciliation to income from continuing operations before disposition of property, condominiums and investment in unconsolidated affiliates and equity in earnings of unconsolidated affiliates:
Total Assets	$ 167,214								$ 159,200								$ 167,214		$ 159,200		$ 150,174

[1] The amounts presented may not equal to the amounts previously reported in the most recent Form 10-Qs or prior 10-K for each period as a result of discontinued operations.

[2] Net of discontinued operations.

[3] Negative NOI with no corresponding revenues represents expensed real estate taxes and other carrying costs associated with land held for development that is currently zoned for the respective product type.