Segments - Net sales by major geographic area (Details) $ in Thousands	3 Months Ended
	Jul. 31, 2020 USD ($) $ / $	Jul. 31, 2019 USD ($) $ / $
Revenues from External Customers and Long-Lived Assets [Line Items]
Total net sales	$ 802,573	$ 847,176
Average exchange rates | $ / $	0.7308	0.7518
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Total net sales	$ 679,321	$ 731,343
Canada
Revenues from External Customers and Long-Lived Assets [Line Items]
Total net sales	$ 123,252	$ 115,833