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Property, Plant and Equipment - Components of Property, Plant and Equipment (Parenthetical) (Detail) - USD ($)
$ in Millions
 12 Months Ended
Mar. 31, 2017
Mar. 31, 2016
Mar. 31, 2015
Property, Plant and Equipment [Line Items]      
Capitalized interest $ 2.0 $ 3.2 $ 1.7
Net book value of disposals 15.0    
Net book value of disposals, usage of replacement parts 13.1    
Net book value of disposals, impairment charges 0.5    
Net book value of disposals, disposal of assets no longer in use 1.4    
Buildings [Member]      
Property, Plant and Equipment [Line Items]      
Buildings held for sale $ 4.5