Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Segment Reporting [Abstract]
Limit of consolidated revenue generated by any single customer									10.00%
Segment Reporting Information [Line Items]
Rental and other revenues	$ 148,988	$ 144,827	$ 132,618	$ 130,377	$ 126,316	$ 120,456	$ 120,423	$ 117,851	$ 556,810		$ 485,046		$ 431,956
Total net operating income									353,466		308,302		274,650
Reconciliation to income from continuing operations before disposition of property, condominiums and investments in unconsolidated affiliates and equity in earnings of unconsolidated affiliates:
Depreciation and amortization									(176,957)		(146,357)		(127,499)
General and administrative expense									(37,193)		(37,377)		(35,727)
Interest expense									(92,703)		(96,114)		(95,510)
Other income									6,398		6,380		7,363
Income from continuing operations before disposition of investment properties and activity in unconsolidated affiliates									53,011		34,834		23,277
Total Assets	3,807,101				3,350,428				3,807,101		3,350,428
Office Total Segment [Member]
Segment Reporting Information [Line Items]
Rental and other revenues									505,937	[1]	434,531	[1]	384,904	[1]
Total net operating income									321,040	[1]	276,446	[1]	245,506	[1]
Reconciliation to income from continuing operations before disposition of property, condominiums and investments in unconsolidated affiliates and equity in earnings of unconsolidated affiliates:
Total Assets	3,425,874				2,828,796				3,425,874		2,828,796
Office Atlanta, GA [Member]
Segment Reporting Information [Line Items]
Rental and other revenues									80,330		60,474		48,839
Total net operating income									49,650		38,186		30,513
Reconciliation to income from continuing operations before disposition of property, condominiums and investments in unconsolidated affiliates and equity in earnings of unconsolidated affiliates:
Total Assets	699,263				495,175				699,263		495,175
Office Greenville, SC [Member]
Segment Reporting Information [Line Items]
Rental and other revenues									3,399		3,269		3,168
Total net operating income									1,893		1,701		1,693
Reconciliation to income from continuing operations before disposition of property, condominiums and investments in unconsolidated affiliates and equity in earnings of unconsolidated affiliates:
Total Assets	15,890				69,138				15,890		69,138
Office Kansas City, MO [Member]
Segment Reporting Information [Line Items]
Rental and other revenues									16,303		14,995		13,789
Total net operating income									10,694		9,509		8,370
Reconciliation to income from continuing operations before disposition of property, condominiums and investments in unconsolidated affiliates and equity in earnings of unconsolidated affiliates:
Total Assets	83,124				84,538				83,124		84,538
Office Memphis, TN [Member]
Segment Reporting Information [Line Items]
Rental and other revenues									38,369		36,812		36,787
Total net operating income									22,133		21,831		20,862
Reconciliation to income from continuing operations before disposition of property, condominiums and investments in unconsolidated affiliates and equity in earnings of unconsolidated affiliates:
Total Assets	249,479				225,541				249,479		225,541
Office Nashville, TN [Member]
Segment Reporting Information [Line Items]
Rental and other revenues									62,054		56,512		53,621
Total net operating income									42,598		38,801		36,566
Reconciliation to income from continuing operations before disposition of property, condominiums and investments in unconsolidated affiliates and equity in earnings of unconsolidated affiliates:
Total Assets	490,887				314,705				490,887		314,705
Office Orlando, FL [Member]
Segment Reporting Information [Line Items]
Rental and other revenues									21,798		9,052		8,099
Total net operating income									12,048		4,334		3,788
Reconciliation to income from continuing operations before disposition of property, condominiums and investments in unconsolidated affiliates and equity in earnings of unconsolidated affiliates:
Total Assets	226,314				51,373				226,314		51,373
Office Piedmont Triad, NC [Member]
Segment Reporting Information [Line Items]
Rental and other revenues									26,047		19,489		18,456
Total net operating income									16,788		12,282		11,835
Reconciliation to income from continuing operations before disposition of property, condominiums and investments in unconsolidated affiliates and equity in earnings of unconsolidated affiliates:
Total Assets	164,885				144,404				164,885		144,404
Office Pittsburgh, PA [Member]
Segment Reporting Information [Line Items]
Rental and other revenues									56,125		38,776		10,964
Total net operating income									31,134		19,530		5,452
Reconciliation to income from continuing operations before disposition of property, condominiums and investments in unconsolidated affiliates and equity in earnings of unconsolidated affiliates:
Total Assets	335,798				330,975				335,798		330,975
Office Raleigh, NC [Member]
Segment Reporting Information [Line Items]
Rental and other revenues									85,417		81,581		78,606
Total net operating income									60,075		56,584		54,670
Reconciliation to income from continuing operations before disposition of property, condominiums and investments in unconsolidated affiliates and equity in earnings of unconsolidated affiliates:
Total Assets	494,208				479,995				494,208		479,995
Office Richmond, VA [Member]
Segment Reporting Information [Line Items]
Rental and other revenues									47,576		47,284		47,505
Total net operating income									32,454		32,382		31,265
Reconciliation to income from continuing operations before disposition of property, condominiums and investments in unconsolidated affiliates and equity in earnings of unconsolidated affiliates:
Total Assets	241,739				246,276				241,739		246,276
Office Tampa, FL [Member]
Segment Reporting Information [Line Items]
Rental and other revenues									68,519		66,287		65,070
Total net operating income									41,573		41,306		40,492
Reconciliation to income from continuing operations before disposition of property, condominiums and investments in unconsolidated affiliates and equity in earnings of unconsolidated affiliates:
Total Assets	424,287				386,676				424,287		386,676
Industrial Total Segment [Member]
Segment Reporting Information [Line Items]
Rental and other revenues									12,997	[1]	13,324	[1]	12,797	[1]
Total net operating income									9,429	[1]	9,610	[1]	9,268	[1]
Reconciliation to income from continuing operations before disposition of property, condominiums and investments in unconsolidated affiliates and equity in earnings of unconsolidated affiliates:
Total Assets	100,772				191,343				100,772		191,343
Industrial Atlanta, GA [Member]
Segment Reporting Information [Line Items]
Rental and other revenues									827		812		975
Total net operating income									492		468		620
Reconciliation to income from continuing operations before disposition of property, condominiums and investments in unconsolidated affiliates and equity in earnings of unconsolidated affiliates:
Total Assets	25,936				115,330				25,936		115,330
Industrial Piedmont Triad, NC [Member]
Segment Reporting Information [Line Items]
Rental and other revenues									12,170		12,512		11,822
Total net operating income									8,937		9,142		8,648
Reconciliation to income from continuing operations before disposition of property, condominiums and investments in unconsolidated affiliates and equity in earnings of unconsolidated affiliates:
Total Assets	74,836				76,013				74,836		76,013
Total Retail Segment [Member]
Segment Reporting Information [Line Items]
Rental and other revenues									37,876	[1]	37,191	[1]	34,255	[1]
Total net operating income									23,074	[1]	22,510	[1]	20,147	[1]
Reconciliation to income from continuing operations before disposition of property, condominiums and investments in unconsolidated affiliates and equity in earnings of unconsolidated affiliates:
Total Assets	161,779				166,030				161,779		166,030
Retail Kansas City, MO [Member]
Segment Reporting Information [Line Items]
Rental and other revenues									37,876		37,191		34,255
Total net operating income									23,074		22,510		20,147
Reconciliation to income from continuing operations before disposition of property, condominiums and investments in unconsolidated affiliates and equity in earnings of unconsolidated affiliates:
Total Assets	161,779				166,030				161,779		166,030
Total Residential Segment [Member]
Segment Reporting Information [Line Items]
Total net operating income									0	[1]	(178)	[1]	(195)	[1]
Reconciliation to income from continuing operations before disposition of property, condominiums and investments in unconsolidated affiliates and equity in earnings of unconsolidated affiliates:
Total Assets	0				8				0		8
Residential Raleigh, NC [Member]
Segment Reporting Information [Line Items]
Total net operating income									0		(178)		(195)
Reconciliation to income from continuing operations before disposition of property, condominiums and investments in unconsolidated affiliates and equity in earnings of unconsolidated affiliates:
Total Assets	0				8				0		8
Total Corporate and Other Segment [Member]
Segment Reporting Information [Line Items]
Total net operating income									(77)	[1]	(86)	[1]	(76)	[1]
Reconciliation to income from continuing operations before disposition of property, condominiums and investments in unconsolidated affiliates and equity in earnings of unconsolidated affiliates:
Total Assets	$ 118,676				$ 164,251				$ 118,676		$ 164,251

[1] Net of discontinued operations.