Debt - Summary of Hedge Notes (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	9 Months Ended
	Oct. 31, 2014
0.75% Note Hedges
Derivatives, Fair Value [Line Items]
Purchase	$ 126,500
Shares	26,943,812
Contractual interest rate	0.75%
0.25% Note Hedges
Derivatives, Fair Value [Line Items]
Purchase	$ 153,800
Shares	17,308,880