Information Regarding All Stock Options (Detail) (USD $)	12 Months Ended
Jan. 31, 2013	Jan. 31, 2012	Jan. 31, 2011
Shares
Stock options outstanding at beginning of year	417,722	514,190	817,050
Exercised	(120,518)	(60,668)	(339,010)
Granted	85,000	40,000	38,000
Cancelled or forfeited	(150)	(75,800)	(1,850)
Stock options outstanding at end of year	382,054	417,722	514,190
Exercisable	224,121	245,556	260,990
Weighted Average Exercise Price
Stock options outstanding at beginning of year	$ 16.59	$ 14.54	$ 11.23
Exercised	$ 11.82	$ 10.21	$ 8.23
Granted	$ 28.72	$ 27.13	$ 29.59
Cancelled or forfeited	$ 18.40	$ 13.35	$ 18.40
Stock options outstanding at end of year	$ 20.79	$ 16.59	$ 14.54
Exercisable	$ 16.89	$ 14.18	$ 12.32

The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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For presentations that combine terminations, the number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan or that expired.

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The number of shares reserved for issuance under stock option agreements awarded under the plan that validly exist and are outstanding as of the balance sheet date, including vested options.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Number of share options (or share units) exercised during the current period.

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