Quarterly report pursuant to Section 13 or 15(d)

Plant Closure Expenses - Schedule of Closure-Related Expenses (Details)

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Plant Closure Expenses - Schedule of Closure-Related Expenses (Details) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2018
Jun. 30, 2018
Restructuring Cost and Reserve [Line Items]    
Cash expenses $ 0.4 $ 1.5
Decommissioning costs    
Restructuring Cost and Reserve [Line Items]    
Cash expenses 0.2 1.0
Contract termination costs    
Restructuring Cost and Reserve [Line Items]    
Cash expenses $ 0.2 $ 0.5