Notes Payable - Principal Amount, Unamortized Debt Discount, Net Carrying Amount of the Liability Component, and Carrying Amount of the Equity Component of the 4.00% Debentures (Detail) (4.00% Debentures due 2031, USD $) In Thousands, unless otherwise specified	Jul. 31, 2014	Jan. 31, 2014
4.00% Debentures due 2031
Debt Instrument
Principal amount	$ 253,000	$ 253,000
Unamortized debt discount	(25,724)	(28,739)
Net carrying amount of the liability component	227,276	224,261
Equity component	$ 43,930	$ 43,930