Earnings Per Share (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended
Oct. 31, 2011	Oct. 31, 2010	Oct. 31, 2011	Oct. 31, 2010
Reconciliation of numerators and denominators for basic and diluted EPS computations
Net earnings for basic and diluted EPS	$ 89,689	$ 55,079	$ 260,795	$ 187,179
Weighted-average shares for basic EPS	127,210	126,176	127,614	126,591
Incremental shares based upon the assumed exercise of stock options and unvested restricted stock units	1,602	1,729	1,715	1,686
Weighted-average shares for diluted EPS	128,812	127,905	129,329	128,277

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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Reference 9: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

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-Glossary Other Comprehensive Income

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Reference 12: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

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-Glossary Net Income

-URI http://asc.fasb.org/extlink&oid=6518256

Reference 13: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

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-Publisher SEC

-Name Regulation S-X (SX)

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+ Details

- Definition

The sum of dilutive potential common shares or units used in the calculation of the diluted per-share or per-unit computation.

+ References+ Details

- Definition

The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

+ References+ Details

- Definition

Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period.

+ References

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+ Details