Summary of Significant Accounting Policies - Estimated Useful Lives of Various Classes of Assets (Detail)	12 Months Ended
	Mar. 31, 2015
Buildings
Property, Plant and Equipment [Line Items]
Estimated useful lives	20 years
Machinery and Equipment
Property, Plant and Equipment [Line Items]
Estimated useful lives	10 years
Yard improvements | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful lives	5 years
Yard improvements | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives	10 years
Loaders and other rolling stock | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful lives	5 years
Loaders and other rolling stock | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives	10 years