Long - Term Debt - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2018	Jan. 31, 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	1,354	$ 2,486	2,766	$ 5,046
Fees to secure the facility, amortized amount			$ 785	785
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	417,675		417,675
Interest expense	$ 547	$ 1,826	$ 1,158	$ 3,704
Weighted-average interest rate on borrowings	2.70%	2.23%	2.63%	2.19%
Fees to secure the facility, amount incurred					$ 7,850
Fees to secure the facility, unamortized amount	$ 5,364		$ 5,364			$ 6,149
Asset-based revolving credit facility | Interest expense
Line of Credit Facility [Line Items]
Fees to secure the facility, amortized amount	$ 392	$ 392	$ 785	$ 785
Asset-based revolving credit facility | Maximum
Line of Credit Facility [Line Items]
Fees to secure the facility, amortization period			5 years