Commitments and Contingencies (Details) (USD $)	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011
Loss Contingencies [Line Items]
Guaranteed Repayment of Economic Development Bonds	$ 83,800,000
Number of unconsolidated subsidiaries for which loans guaranteed	5
Maximum Guarantee Exposure for Joint Venture Loans	247,100,000
Variable Interest Entity, Nonconsolidated, Carrying Amount, Liabilities	23,300,000	[1]	17,700,000	[1]
Total obligation for operating leases for certain land positions	206,500,000
Other Liabilities	167,935,000		131,735,000
3630 Peachtree Joint Venture [Member]
Loss Contingencies [Line Items]
Variable Interest Entity, Nonconsolidated, Carrying Amount, Liabilities	(17,300,000)
Special Tax Assessment [Member]
Loss Contingencies [Line Items]
Other Liabilities	$ 12,500,000

[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. We have also recorded a liability for our probable future obligation under a guarantee to the lender of one of these ventures, which is included within the carrying value of our guarantee obligations. 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 Sheet