Summary of Interest Expense Related to Convertible Notes (Detail) (5.25% Convertible Senior Notes due 2019, USD $) In Thousands, unless otherwise specified	3 Months Ended	6 Months Ended
	Jan. 31, 2015	Jan. 31, 2015
Non Cash Convertible Debt Related Expense [Line Items]
Debt instrument, interest expense	$ 2,552	$ 4,983
Coupon interest rate
Non Cash Convertible Debt Related Expense [Line Items]
Debt instrument, interest expense	1,313	2,626
Accretion of debt discount
Non Cash Convertible Debt Related Expense [Line Items]
Debt instrument, interest expense	1,142	2,169
Amortization of debt issue cost
Non Cash Convertible Debt Related Expense [Line Items]
Debt instrument, interest expense	$ 97	$ 188