Long - Term Debt - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended		12 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2017	Jan. 31, 2016	Jul. 31, 2016
Line of Credit Facility [Line Items]
Line of credit, outstanding amount	$ 325,000,000		$ 325,000,000		$ 360,000,000
Interest expense	2,486,000	$ 168,000	5,046,000	$ 342,000
Fees to secure the facility, amortized amount			$ 785,000
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, current borrowing capacity	500,000,000		$ 500,000,000
Line of credit, entitled expansion option	100,000,000		100,000,000
Line of credit, outstanding amount	325,000,000		$ 325,000,000		360,000,000
Line of credit, percentage of annual fee on unused portion of the facility			0.25%
Line of credit, frequency of annual fee payment on unused portion of the facility			Quarterly
Line of credit, borrowing availability	137,561,000		$ 137,561,000
Line of credit, borrowing availability term			Borrowing availability under the credit agreement is limited to the lesser of the facility total and the monthly calculated borrowing base
Line of credit, covenant term			The credit agreement has no financial covenant restrictions for borrowings as long as the Company has adjusted excess availability under the facility that exceeds 10% of the lesser of the line commitment or the borrowing base total, with a floor of $40,000.
Line of credit, fixed charge coverage ratio			100.00%
Line of credit, adjusted excess availability for covenant purpose	$ 238,536,000		$ 238,536,000
Weighted-average interest rate on borrowings	2.23%		2.19%
Fees to secure the facility, amount incurred					$ 7,850,000
Fees to secure the facility, unamortized amount	$ 6,934,000		$ 6,934,000
Asset-based revolving credit facility | Interest expense
Line of Credit Facility [Line Items]
Fees to secure the facility, amortized amount	392,000		$ 785,000
Asset-based revolving credit facility | Minimum
Line of Credit Facility [Line Items]
Line of credit, percentage of line commitment to be exceeded by the excess borrowing availability			10.00%
Line of credit, borrowing base	40,000,000		$ 40,000,000
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 rate
Line of Credit Facility [Line Items]
Line of credit, outstanding amount	$ 320,000,000		$ 320,000,000
Line of credit, pricing spreads rate			1.50%
Line of credit, effective interest rate	2.27%		2.27%
Asset-based revolving credit facility | LIBOR rate | Minimum
Line of Credit Facility [Line Items]
Line of credit, pricing spreads rate			1.25%
Asset-based revolving credit facility | LIBOR rate | Maximum
Line of Credit Facility [Line Items]
Line of credit, pricing spreads rate			1.75%
Asset-based revolving credit facility | Base rate
Line of Credit Facility [Line Items]
Line of credit, outstanding amount	$ 5,000,000		$ 5,000,000
Line of credit, pricing spreads rate			0.50%
Line of credit, effective interest rate	4.25%		4.25%
Asset-based revolving credit facility | Base rate | Minimum
Line of Credit Facility [Line Items]
Line of credit, pricing spreads rate			0.25%
Asset-based revolving credit facility | Base rate | Maximum
Line of Credit Facility [Line Items]
Line of credit, pricing spreads rate			0.75%
Asset-based revolving credit facility | LIBOR and base rate
Line of Credit Facility [Line Items]
Interest expense	$ 1,826,000		$ 3,704,000