Earnings Per Share (Details) (USD $) In Thousands, except Share data	3 Months Ended		6 Months Ended
	Jul. 31, 2011	Jul. 31, 2010	Jul. 31, 2011	Jul. 31, 2010
Reconciliation of numerators and denominators for basic and diluted EPS computations
Net earnings for basic and diluted EPS	$ 90,043	$ 67,675	$ 171,106	$ 132,100
Weighted-average shares for basic EPS	128,030,000	126,897,000	127,816,000	126,798,000
Incremental shares based upon the assumed exercise of stock options and unvested restricted stock units	1,764,000	1,488,000	1,771,000	1,666,000
Weighted-average shares for diluted EPS	129,794,000	128,385,000	129,587,000	128,464,000
Earnings Per Share (Textuals)
Antidilutive stock options and restricted stock units excluded from the computations of earnings per diluted share	351,000	487,000	332,000	459,000