Stock Option Plans (Detail) (USD $) In Millions, except Share data, unless otherwise specified	6 Months Ended
	Jul. 31, 2012	Jul. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Total Intrinsic Value	$ 1.8	$ 3.1
Tax Benefit from Stock Options Exercised	$ 0.3	$ 0.6
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period (in Shares)	(99,968)	32,935
Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price (in Dollars per share)	$ 14.30	$ 32.53