Impairments and Other Charges Impairments and Other Charges (Narrative) (Details) (USD $)	12 Months Ended																		3 Months Ended	2 Months Ended
	Dec. 31, 2011	Dec. 31, 2010		Dec. 31, 2009 buildings A	Dec. 31, 2011 Land Impairment [Member]	Dec. 31, 2010 Land Impairment [Member]	Dec. 31, 2009 Land Impairment [Member]	Dec. 31, 2011 Building Impairment [Member]	Dec. 31, 2010 Building Impairment [Member]	Dec. 31, 2009 Building Impairment [Member]	Dec. 31, 2011 Unconsolidated JV Impairment [Member]	Dec. 31, 2010 Unconsolidated JV Impairment [Member]	Dec. 31, 2009 Unconsolidated JV Impairment [Member]	Dec. 31, 2011 Other Real Estate Related Impairment [Member]	Dec. 31, 2010 Other Real Estate Related Impairment [Member]	Dec. 31, 2009 Other Real Estate Related Impairment [Member]	Dec. 31, 2009 Income Approach [Member] buildings	Dec. 31, 2009 Market Approach [Member] buildings	Sep. 30, 2009 3630 Peachtree Joint Venture [Member]	Jun. 30, 2009 Park Creek Joint Venture [Member]
Operating Lease Receivables [Line Items]
Asset impairment charges	$ 12,931,000	$ 9,834,000		$ 302,566,000	$ 12,931,000	$ 9,834,000	$ 136,581,000	$ 0	$ 0	$ 78,087,000	$ 0	$ 0	$ 56,437,000	$ 0	$ 0	$ 31,461,000
Less: Impairment charges included in discontinued operations	0	0		(27,206,000)
Continuing Operations Asset Impairment Charges	12,931,000	9,834,000		275,360,000
Carrying value of assets evaluated for impairment				385,300,000
Acres of land evaluated for impairment				1,800
Number of real estate properties determined to be impaired				28													16	12
Number of real estate properties sold after determined to be impaired																		11
Impairment charge on investment in joint venture																			14,400,000	5,800,000
Liability for probable future obligation to unconsolidated entity	$ 17,700,000	$ 25,200,000	[1]	$ 36,300,000

[1] We are party to guarantees of the third-party debt of these joint ventures and our maximum loss exposure is equal to the maximum monetary obligation pursuant to the guarantee agreements. In 2009, we recorded a liability for our probable future obligation under a guarantee to the lender of one of these ventures. Pursuant to an agreement with the lender, we may make partner loans to this joint venture that will reduce our maximum guarantee obligation on a dollar-for-dollar basis. The carrying value of our recorded guarantee obligations is included in other liabilities in our Consolidated Balance Sheets.