Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012		Mar. 31, 2011
Segment Reporting Information [Line Items]
Total Rental and Other Revenues	$ 129,943		$ 114,351
Total Net Operating Income	83,819		73,417
Reconciliation to income from continuing operations before disposition of condominiums and equity in earnings/(losses) of unconsolidated affiliates:
Depreciation and amortization	(38,362)		(33,556)
General and administrative expense	(9,673)		(7,793)
Interest expense	(24,802)		(23,543)
Interest and other income	2,230		1,873
Income from continuing operations before disposition of condominiums and equity in earnings/(losses) of unconsolidated affiliates	13,212		10,398
Total Office Segment [Member]
Segment Reporting Information [Line Items]
Total Rental and Other Revenues	114,079	[1]	98,542	[1]
Total Net Operating Income	73,106	[1]	63,068	[1]
Office Atlanta, GA [Member]
Segment Reporting Information [Line Items]
Total Rental and Other Revenues	15,785		11,902
Total Net Operating Income	10,396		7,493
Office Greenville, SC [Member]
Segment Reporting Information [Line Items]
Total Rental and Other Revenues	3,504		3,505
Total Net Operating Income	2,133		2,075
Office Kansas City, MO [Member]
Segment Reporting Information [Line Items]
Total Rental and Other Revenues	3,762		3,657
Total Net Operating Income	2,362		2,114
Office Memphis, TN [Member]
Segment Reporting Information [Line Items]
Total Rental and Other Revenues	10,139		10,103
Total Net Operating Income	6,103		5,759
Office Nashville, TN [Member]
Segment Reporting Information [Line Items]
Total Rental and Other Revenues	15,603		14,616
Total Net Operating Income	10,603		9,651
Office Orlando, FL [Member]
Segment Reporting Information [Line Items]
Total Rental and Other Revenues	2,688		2,318
Total Net Operating Income	1,416		1,166
Office Piedmont Triad, NC [Member]
Segment Reporting Information [Line Items]
Total Rental and Other Revenues	5,081		5,364
Total Net Operating Income	3,233		3,600
Office Pittsburgh, PA [Member]
Segment Reporting Information [Line Items]
Total Rental and Other Revenues	9,087		0
Total Net Operating Income	4,282		0
Office Raleigh, NC [Member]
Segment Reporting Information [Line Items]
Total Rental and Other Revenues	19,781		19,322
Total Net Operating Income	13,854		13,219
Office Richmond, VA [Member]
Segment Reporting Information [Line Items]
Total Rental and Other Revenues	11,511		11,379
Total Net Operating Income	7,884		7,861
Office Tampa, FL [Member]
Segment Reporting Information [Line Items]
Total Rental and Other Revenues	17,138		16,376
Total Net Operating Income	10,840		10,130
Total Industrial Segment [Member]
Segment Reporting Information [Line Items]
Total Rental and Other Revenues	6,939	[1]	6,911	[1]
Total Net Operating Income	5,177	[1]	5,062	[1]
Industrial Atlanta, GA [Member]
Segment Reporting Information [Line Items]
Total Rental and Other Revenues	3,774		3,934
Total Net Operating Income	2,889		2,839
Industrial Piedmont Triad, NC [Member]
Segment Reporting Information [Line Items]
Total Rental and Other Revenues	3,165		2,977
Total Net Operating Income	2,288		2,223
Total Retail Segment [Member]
Segment Reporting Information [Line Items]
Total Rental and Other Revenues	8,925	[1]	8,898	[1]
Total Net Operating Income	5,536	[1]	5,287	[1]
Retail Kansas City, MO [Member]
Segment Reporting Information [Line Items]
Total Rental and Other Revenues	8,925		8,898
Total Net Operating Income	$ 5,536		$ 5,287

[1] Net of discontinued operations.