Short-Term and Long-Term Debt - Summary of Notes Due 2020 (Details) (USD $) In Thousands, unless otherwise specified	Jul. 31, 2014
Debt Instrument [Line Items]
Liability component, Unamortized discount	$ 1,237
4.0% Convertible Senior Notes due December 15, 2020
Debt Instrument [Line Items]
Interest rate on convertible notes	4.00%
Convertible Notes Payable | 4.0% Convertible Senior Notes due December 15, 2020
Debt Instrument [Line Items]
Liability component, Principal balance	193,101
Liability component, Unamortized discount	15,248
Liability component, Net carrying amount	177,853
Equity component, Net carrying amount	$ 43,131