Summary of Interest Expense Related to Convertible Notes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Jul. 31, 2016	Jul. 31, 2015	Jul. 31, 2014
Non Cash Convertible Debt Related Expense [Line Items]
Debt instrument, interest expense	$ 4,967	$ 4,473	$ 1,489
5.25% Convertible Senior Notes due 2019
Non Cash Convertible Debt Related Expense [Line Items]
Debt instrument, interest expense	10,565	10,127
5.25% Convertible Senior Notes due 2019 | Coupon Interest
Non Cash Convertible Debt Related Expense [Line Items]
Debt instrument, interest expense	5,159	5,310
5.25% Convertible Senior Notes due 2019 | Accretion of debt discount
Non Cash Convertible Debt Related Expense [Line Items]
Debt instrument, interest expense	4,967	4,473
5.25% Convertible Senior Notes due 2019 | Amortization of debt issue cost
Non Cash Convertible Debt Related Expense [Line Items]
Debt instrument, interest expense	$ 439	$ 344