Summarized Quarterly Financial Data (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Jan. 31, 2013	Oct. 31, 2012	Jul. 31, 2012	Apr. 30, 2012	Jan. 31, 2012	Oct. 31, 2011	Jul. 31, 2011	Apr. 30, 2011	Jan. 31, 2013	Jan. 31, 2012	Jan. 31, 2011
Quarterly Financial Information [Line Items]
Net sales	$ 375,278	$ 543,513	$ 251,479	$ 229,449	$ 294,346	$ 510,009	$ 229,975	$ 196,871	$ 1,399,719	$ 1,231,201	$ 1,063,404
Gross profit	117,897	190,207	74,843	68,690	83,415	162,275	65,571	59,455	451,637	370,716	351,045
Net income/(loss)	$ 8,070	$ 48,291	$ 1,362	$ (847)	$ 5,020	$ 43,555	$ 1,565	$ (520)	$ 56,569	$ 49,620	$ 56,682
Net income/(loss) per common share
Basic	$ 0.40	$ 2.41	$ 0.07	$ (0.04)	$ 0.25	$ 2.19	$ 0.08	$ (0.03)	$ 2.84	$ 2.51	$ 2.96
Diluted	$ 0.40	$ 2.37	$ 0.07	$ (0.04)	$ 0.25	$ 2.16	$ 0.08	$ (0.03)	$ 2.80	$ 2.46	$ 2.88