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Summary of Interest Expense Related to Convertible Notes (Detail) - 5.25% Convertible Senior Notes due 2019 - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Jan. 31, 2016
Jan. 31, 2015
Jan. 31, 2016
Jan. 31, 2015
Non Cash Convertible Debt Related Expense [Line Items]        
Debt instrument, interest expense $ 2,692 $ 2,552 $ 5,338 $ 4,983
Coupon interest rate        
Non Cash Convertible Debt Related Expense [Line Items]        
Debt instrument, interest expense 1,323 1,313 2,646 2,626
Accretion of debt discount        
Non Cash Convertible Debt Related Expense [Line Items]        
Debt instrument, interest expense 1,258 1,142 2,473 2,169
Amortization of debt issue cost        
Non Cash Convertible Debt Related Expense [Line Items]        
Debt instrument, interest expense $ 111 $ 97 $ 219 $ 188