Property Transactions (Properties Held for Sale) (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 from discontinued operations	$ 19,358	$ 11,489	$ 18,407
777 Main Fort Worth, TX [Member]
Summary of sales in discontinued operations
Area of disposed real estate assets (square feet)	980,000
Sales price of property held for sale, discontinued operations	167,000
Third party management and leasing business [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain on sale from discontinued operations	(3)	4,577	7,459
Tiffany Springs MarketCenter Kansas City [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain on sale from discontinued operations	(1)	3,697	0
Summary of sales in discontinued operations
Area of disposed real estate assets (square feet)		238,000
Sales price of property held for sale, discontinued operations		53,500
Lakeshore Park Plaza Birmingham [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain on sale from discontinued operations	13,025	0	0
Summary of sales in discontinued operations
Area of disposed real estate assets (square feet)	197,000
Sales price of property held for sale, discontinued operations	25,000
Mahan Village Tallahassee FL [Member]
Summary of sales in discontinued operations
Area of disposed real estate assets (square feet)	147,000
Sales price of property held for sale, discontinued operations	29,500
Six Hundred University Park Place Birmingham [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain on sale from discontinued operations	6,334	0	0
Summary of sales in discontinued operations
Area of disposed real estate assets (square feet)	123,000
Sales price of property held for sale, discontinued operations	19,700
The Avenue Forsyth Suburban Atlanta, GA [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain on sale from discontinued operations	1	(77)	4,508
Summary of sales in discontinued operations
Area of disposed real estate assets (square feet)			524,000
Sales price of property held for sale, discontinued operations			119,000
The Avenue Collierville [Member]
Summary of sales in discontinued operations
Area of disposed real estate assets (square feet)			511,000
Sales price of property held for sale, discontinued operations			55,000
The Avenue Webb Gin Suburban Atlanta, GA [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain on sale from discontinued operations	0	(2)	3,590
Summary of sales in discontinued operations
Area of disposed real estate assets (square feet)			322,000
Sales price of property held for sale, discontinued operations			59,600
Galleria 75 [Member]
Summary of sales in discontinued operations
Area of disposed real estate assets (square feet)			111,000
Sales price of property held for sale, discontinued operations			9,200
Cosmopolitan Center [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain on sale from discontinued operations	0	0	2,064
Summary of sales in discontinued operations
Area of disposed real estate assets (square feet)			51,000
Sales price of property held for sale, discontinued operations			7,000
Inhibitex Suburban Atlanta, GA [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain on sale from discontinued operations	2	2,989	0
Summary of sales in discontinued operations
Area of disposed real estate assets (square feet)		51,000
Sales price of property held for sale, discontinued operations		$ 8,300