Leases - Supplemental cash flow information (Details) - USD ($) $ in Thousands	3 Months Ended
	Jul. 31, 2020	Jul. 31, 2019
Cash paid for amounts included in the measurement of lease liabilities
Operating cash flows from operating leases	$ 10,648	$ 10,236
Operating cash flows from finance leases	3,062	3,422
Financing cash flows from finance leases	7,521	6,021
Right-of-use assets obtained in exchange for lease obligations - Operating leases	6,843	6,241
Right-of-use assets obtained in exchange for lease obligations - Finance leases	$ 3,935	$ 11,874