Earnings Per Share (Details) (USD $)	3 Months Ended		6 Months Ended
	Jul. 31, 2014	Jul. 31, 2013	Jul. 31, 2014	Jul. 31, 2013
Earnings Per Share [Abstract]
Net earnings	$ 124,120,000	$ 106,781,000	$ 249,729,000	$ 190,358,000
Basic	129,252,000	127,826,000	129,093,000	127,572,000
Incremental shares based upon assumed exercise of stock options and unvested restricted stock units	656,000	945,000	758,000	1,034,000
Diluted	129,908,000	128,771,000	129,851,000	128,606,000
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	347,000	412,000	336,000	589,000