Property Transactions (Gain (Loss) on Sales of Discontinued Operations) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Document Fiscal Year Focus	2014	2013	2012
Gain on sale of investment properties included in discontinued operations
Gain on sale of discontinued investment properties	$ 19,358	$ 11,489	$ 18,407
Lakeshore Park Plaza Birmingham [Member]
Gain on sale of investment properties included in discontinued operations
Gain on sale of discontinued investment properties	13,025	0	0
Six Hundred University Park Place Birmingham [Member]
Gain on sale of investment properties included in discontinued operations
Gain on sale of discontinued investment properties	6,334	0	0
The Avenue Forsyth Suburban Atlanta, GA [Member]
Gain on sale of investment properties included in discontinued operations
Gain on sale of discontinued investment properties	1	(77)	4,508
Inhibitex Suburban Atlanta [Member]
Gain on sale of investment properties included in discontinued operations
Gain on sale of discontinued investment properties	2	2,989	0
Tiffany Springs MarketCenter Kansas City [Member]
Gain on sale of investment properties included in discontinued operations
Gain on sale of discontinued investment properties	(1)	3,697	0
Third party management and leasing business [Member]
Gain on sale of investment properties included in discontinued operations
Gain on sale of discontinued investment properties	(3)	4,577	7,459
Cosmopolitan Center [Member]
Gain on sale of investment properties included in discontinued operations
Gain on sale of discontinued investment properties	0	0	2,064
Avenue Webb Gin Suburban Atlanta [Member]
Gain on sale of investment properties included in discontinued operations
Gain on sale of discontinued investment properties	0	(2)	3,590
Other Disposal Groups [Member]
Gain on sale of investment properties included in discontinued operations
Gain on sale of discontinued investment properties	$ 0	$ 305	$ 786