Segments - Net sales by major geographic area (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Apr. 30, 2021	Jan. 31, 2021	Oct. 31, 2020	Jul. 31, 2020	Apr. 30, 2020	Jan. 31, 2020	Oct. 31, 2019	Jul. 31, 2019	Apr. 30, 2021	Apr. 30, 2020	Apr. 30, 2019
Revenues from External Customers and Long-Lived Assets [Line Items]
Total net sales	$ 932,203	$ 751,191	$ 812,856	$ 802,573	$ 770,850	$ 761,352	$ 861,929	$ 847,176	$ 3,298,823	$ 3,241,307	$ 3,116,032
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Total net sales									2,770,450	2,805,920	2,701,678
Canada
Revenues from External Customers and Long-Lived Assets [Line Items]
Total net sales									$ 528,373	$ 435,387	$ 414,354