Debt - Schedule of Convertible Senior Notes (Detail) (USD $) In Thousands, unless otherwise specified	Oct. 31, 2014	Jan. 31, 2014	Oct. 31, 2014 0.75% Convertible Senior Notes due January 15, 2015	Jan. 31, 2014 0.75% Convertible Senior Notes due January 15, 2015	Jan. 31, 2011 0.75% Convertible Senior Notes due January 15, 2015	Oct. 31, 2014 0.25% Convertible Senior Notes due April 1, 2018	Jan. 31, 2014 0.25% Convertible Senior Notes due April 1, 2018	Mar. 31, 2013 0.25% Convertible Senior Notes due April 1, 2018
Debt Instrument [Line Items]
Principal			$ 181,637	$ 568,864		$ 1,150,000	$ 1,150,000
Less: debt discount, net			(1,882)	(26,705)		(85,317)	(103,070)
Net carrying amount	$ 1,244,438	$ 1,589,089
Interest percentage of convertible senior notes			0.75%		0.75%	0.25%		0.25%
Effective interest rates of Senior Notes			5.86%			2.53%