Long - Term Debt - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Apr. 30, 2018	Apr. 30, 2017	Apr. 30, 2018	Apr. 30, 2017	Jul. 31, 2016	Jul. 31, 2017
Line of Credit Facility [Line Items]
Line of credit, outstanding amount	$ 80,000		$ 80,000			$ 145,000
Interest expense	1,383	$ 2,547	4,149	$ 7,593
Fees to secure the facility, amortized amount			$ 1,177	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	80,000		$ 80,000			145,000
Line of credit, borrowing availability	415,808		415,808
Interest expense	$ 584	$ 1,879	$ 1,742	$ 5,583
Weighted-average interest rate on borrowings	2.92%	2.38%	2.72%	2.25%
Fees to secure the facility, amount incurred					$ 7,850
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 | Other Noncurrent Assets [Member]
Line of Credit Facility [Line Items]
Fees to secure the facility, unamortized amount	$ 4,972		$ 4,972			$ 6,149
Asset-based revolving credit facility | Interest expense
Line of Credit Facility [Line Items]
Fees to secure the facility, amortized amount	$ 392	$ 392	$ 1,177	$ 1,177