Earnings Per Share (Details) (USD $)	3 Months Ended		9 Months Ended
	Oct. 31, 2014	Oct. 31, 2013	Oct. 31, 2014	Oct. 31, 2013
Earnings Per Share [Abstract]
Net earnings	$ 38,268,000	$ 94,610,000	$ 287,997,000	$ 284,968,000
Basic	129,352,000	128,004,000	129,179,000	127,716,000
Incremental shares based upon assumed exercise of stock options and unvested restricted stock units	626,000	970,000	715,000	1,013,000
Diluted	129,978,000	128,974,000	129,894,000	128,729,000
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	266,000	350,000	312,000	509,000