Summary of Interest Expense Related to Convertible Notes (Detail) - USD ($) $ in Thousands	3 Months Ended
	Oct. 31, 2018	Oct. 31, 2017
Interest Expense, Debt [Line Items]
Debt instrument, interest expense	$ 1,051	$ 1,041
5.25% Convertible Senior Notes Due 2019
Interest Expense, Debt [Line Items]
Debt instrument, interest expense	1,934	2,047
5.25% Convertible Senior Notes Due 2019 | Coupon Interest
Interest Expense, Debt [Line Items]
Debt instrument, interest expense	790	914
5.25% Convertible Senior Notes Due 2019 | Accretion of Debt Discount
Interest Expense, Debt [Line Items]
Debt instrument, interest expense	1,051	1,041
5.25% Convertible Senior Notes Due 2019 | Amortization of Debt Issue Cost
Interest Expense, Debt [Line Items]
Debt instrument, interest expense	$ 93	$ 92