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Commitments and Contingencies (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2011
Y
Commitments and Contingencies  
Remaining term of operating and ground leases (in years) 89
Future minimum lease obligations under non-cancelable operating and ground leases  
2012 $ 17.6
2013 16.5
2014 15.8
2015 14.0
2016 13.9
Thereafter $ 322.5