Long - Term Debt - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2017	Apr. 30, 2016	Jul. 31, 2016
Line of Credit Facility [Line Items]
Line of credit, outstanding amount	$ 295,000		$ 295,000		$ 360,000
Interest expense	2,547	$ 166	7,593	$ 508
Fees to secure the facility, amortized amount			$ 1,177
Asset-based revolving credit facility
Line of Credit Facility [Line Items]
Line of credit, maturity period			5 years
Line of credit, commencement date			Jun. 30, 2016
Line of credit, maturity date			Jun. 30, 2021
Line of credit, outstanding amount	295,000		$ 295,000		360,000
Line of credit, borrowing availability	$ 202,825		$ 202,825
Weighted-average interest rate on borrowings	2.38%		2.25%
Fees to secure the facility, amount incurred					$ 7,850
Fees to secure the facility, unamortized amount	$ 6,542		$ 6,542
Asset-based revolving credit facility | Interest expense
Line of Credit Facility [Line Items]
Fees to secure the facility, amortized amount	392		$ 1,177
Asset-based revolving credit facility | Maximum
Line of Credit Facility [Line Items]
Fees to secure the facility, amortization period			5 years
Asset-based revolving credit facility | LIBOR and base rate
Line of Credit Facility [Line Items]
Interest expense	$ 1,879		$ 5,583