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Significant Accounting Policies - (Gain) Loss on Disposition of Assets (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Accounting Policies [Abstract]      
Net book value of assets disposed $ 3.3 $ 36.4 $ 12.4
Proceeds from sales (4.8) (27.6) (14.3)
(Gain) loss on disposition of assets $ (1.5) $ 8.8 $ (1.9)