Commitments and Contingencies (Details 1) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Commitments and Contingencies (Textuals) [Abstract]
Commitments for contracts and executed leases, operating and redevelopment and development properties	$ 601.8		$ 601.8
Construction bonds, outstanding	4.4		4.4
Ten Year Ground Lease Extension Option			10 years
Forty-Five Year Ground Lease Extension Option			45 years
Period after which Ground lease rentals are adjusted based on fair market value and the Consumer Price Index			5 years
Annual ground lease rental obligations limit			1.0
Ground Lease, Minimum Rent Increase, Period of Increase			5 years
Ground Lease, Minimum Rent Increase, Percentage of Annual Percentage Rent			50.00%
Proceeds from Bankruptcy Claim	0.9	3.7
Proceeds from Legal Settlements				1.0	3.6
Bad Debt Expense, Recoveries of Bad Debt					1.0
Ten Year Ground Lease Extension Option [Member]
Commitments and Contingencies (Textuals) [Abstract]
Number of extension options			3
Forty-Five Year Ground Lease Extension Option [Member]
Commitments and Contingencies (Textuals) [Abstract]
Number of extension options			1
Other Income [Member]
Commitments and Contingencies (Textuals) [Abstract]
Gain (Loss) Related to Litigation Settlement				$ 4.3