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Summary of Significant Accounting Policies - Derivative Instruments and Hedging Activities Narrative (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Mar. 02, 2020
Derivative [Line Items]        
Mark-to-market gains/(losses) for derivatives $ 0.9 $ (0.4) $ 1.2  
Interest Rate Swap        
Derivative [Line Items]        
Derivative, notional amount $ 1,200.0     $ 1,200.0