Earnings Per Share - Reconciliation of Denominator Used in Calculation of Basic and Diluted Loss Per Share (Detail) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Apr. 30, 2016	Apr. 30, 2015
Earnings Per Share [Abstract]
Net income	$ 38,759	$ 4,092
Weighted-average shares outstanding for basic income per share (in shares)	677,514	653,809
Convertible senior notes (in shares)	945	0
Employee stock awards (in shares)	8,340	10,501
Warrants (in shares)	0	0
Adjusted weighted-average shares outstanding and assumed conversions for diluted income per share (in shares)	686,799	664,310