Significant Accounting Policies - Depreciation of Property and Equipment and Amortization of Capital Lease Assets (Details)	12 Months Ended
	Apr. 30, 2017
Buildings | Minimum
Property, Plant and Equipment
Property, plant and equipment useful life	25 years
Buildings | Maximum
Property, Plant and Equipment
Property, plant and equipment useful life	40 years
Machinery and Equipment | Minimum
Property, Plant and Equipment
Property, plant and equipment useful life	5 years
Machinery and Equipment | Maximum
Property, Plant and Equipment
Property, plant and equipment useful life	30 years