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Intangible Assets - Narrative (Details) (USD $)
In Millions, unless otherwise specified
3 Months Ended 9 Months Ended
Sep. 30, 2014
Sep. 30, 2013
Sep. 30, 2014
Sep. 30, 2013
Finite-Lived Intangible Assets [Line Items]        
Amortization of Intangible Assets $ 22.8 $ 22.6 $ 67.3 $ 68.2
Amortization of direct lease acquisition costs $ 8.8 $ 7.2 $ 24.2 $ 22.7
Minimum
       
Finite-Lived Intangible Assets [Line Items]        
Direct lease acquisition costs, useful life 28 days      
Maximum
       
Finite-Lived Intangible Assets [Line Items]        
Direct lease acquisition costs, useful life 1 year