Short-Term and Long-Term Debt - Summary of Notes Due 2020 (Details) - Convertible Notes Payable - 4.0% Convertible Senior Notes due December 15, 2020 $ in Thousands	Jul. 31, 2015 USD ($)
Debt Instrument [Line Items]
Liability component, Principal balance	$ 196,679
Liability component, Unamortized discount	13,769
Liability component, Net carrying amount	182,910
Equity component, Net carrying amount	$ 43,131