Long-Term Debt - Asset-Based Lending Facility (Details) - USD ($) $ in Thousands	3 Months Ended
	Jul. 31, 2018	Jul. 31, 2017
Long-term debt
Net borrowings	$ 392,170	$ 167,429
ABL Facility
Long-term debt
Maximum amount under the facility	$ 345,000
Borrowing interest rate (as a percent)	4.09%
Available borrowings under the facility	$ 119,800
Net borrowings	215,400
ABL Facility | Swing-line
Long-term debt
Maximum amount under the facility	$ 34,500