Reconciliation of Denominator Used in Calculation of Basic and Diluted Loss Per Share (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Jan. 31, 2014	Oct. 31, 2013	Jul. 31, 2013	Apr. 30, 2013	Jan. 31, 2013	Oct. 31, 2012	Jul. 31, 2012	Apr. 30, 2012	Jan. 31, 2014		Jan. 31, 2013		Jan. 31, 2012
Earnings Per Share [Abstract]
Net loss	$ (116,623)	$ (124,434)	$ 76,603	$ (67,721)	$ (20,844)	$ (220,297)	$ (9,829)	$ (19,475)	$ (232,175)		$ (270,445)		$ (11,572)
Weighted-average shares outstanding for basic loss per share									597,613	[1]	564,896	[1]	541,208	[1]
Convertible senior notes									0		0		0
Employee stock awards									0		0		0
Warrants									0		0		0
Adjusted weighted-average shares outstanding and assumed conversions for diluted loss per share									597,613	[1]	564,896	[1]	541,208	[1]

[1] Prior period results have been adjusted to reflect the four-for-one stock split through a stock dividend which occurred in April 2013.