Segments - Net sales by major geographic area (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Oct. 31, 2018 USD ($) $ / $	Oct. 31, 2017 USD ($) $ / $	Oct. 31, 2018 USD ($) $ / $	Oct. 31, 2017 USD ($) $ / $
Revenues from External Customers and Long-Lived Assets [Line Items]
Total net sales	$ 833,837	$ 648,004	$ 1,611,981	$ 1,290,161
Average exchange rates | $ / $	0.7697	0.7965	0.7679	0.7862
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Total net sales	$ 706,347	$ 648,004	$ 1,397,078	$ 1,290,161
Canada
Revenues from External Customers and Long-Lived Assets [Line Items]
Total net sales	$ 127,490		$ 214,903