Debt - Schedule of Conversion of Senior Notes to Common Stock (Detail) (USD $)	9 Months Ended
	Oct. 31, 2014
0.75% Convertible Senior Notes due January 15, 2015
Debt Instrument [Line Items]
Conversion Rate per $1,000 Par Value	46.8588
Initial Conversion Price per Share	$ 21.34
0.25% Convertible Senior Notes due April 1, 2018
Debt Instrument [Line Items]
Conversion Rate per $1,000 Par Value	15.0512
Initial Conversion Price per Share	$ 66.44