Segments - Net sales by major geographic area (Details) - USD ($) $ in Thousands	3 Months Ended
	Jul. 31, 2018	Jul. 31, 2017
Revenues from External Customers and Long-Lived Assets [Line Items]
Total net sales	$ 778,144	$ 642,157
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Total net sales	690,731	$ 642,157
Canada
Revenues from External Customers and Long-Lived Assets [Line Items]
Total net sales	$ 87,413