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Consolidated Balance Sheets (Parenthetical) - USD ($)
$ in Millions
Mar. 31, 2021
Dec. 31, 2020
Mar. 31, 2020
Current assets      
Allowance for doubtful accounts $ 0.1   $ 0.1
Property, plant and equipment, accumulated depreciation and amortization $ 1,233.6 $ 1,191.4  
Stockholders' Equity      
Preferred stock par value (in dollars per share) $ 0.01 $ 0.01  
Preferred stock shares authorized (in shares) 20,000,000 20,000,000  
Preferred stock shares outstanding (in shares) 0 0  
Common stock par value (in dollars per share) $ 0.01 $ 0.01  
Common stock shares authorized (in shares) 200,000,000 200,000,000  
Common stock shares issued (in shares) 46,767,164 46,767,164  
Treasury stock, shares held (in shares) 19,842,900 19,518,551