Summary of Interest Expense Related to Convertible Notes (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2017	Jan. 31, 2016
Non Cash Convertible Debt Related Expense [Line Items]
Debt instrument, interest expense			$ 1,940	$ 2,473
5.25% Convertible Senior Notes due 2019
Non Cash Convertible Debt Related Expense [Line Items]
Debt instrument, interest expense	$ 1,976	$ 2,692	3,935	5,338
5.25% Convertible Senior Notes due 2019 | Coupon Interest
Non Cash Convertible Debt Related Expense [Line Items]
Debt instrument, interest expense	888	1,323	1,823	2,646
5.25% Convertible Senior Notes due 2019 | Accretion of debt discount
Non Cash Convertible Debt Related Expense [Line Items]
Debt instrument, interest expense	999	1,258	1,940	2,473
5.25% Convertible Senior Notes due 2019 | Amortization of debt issue cost
Non Cash Convertible Debt Related Expense [Line Items]
Debt instrument, interest expense	$ 89	$ 111	$ 172	$ 219