Employee Benefits and Stock-Based Compensation - Stock Option Activities (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
Jan. 31, 2013	Jan. 31, 2012	Jan. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares, Outstanding	4,375,906	3,814,782	2,952,083
Shares, Granted	451,071	1,207,564	1,024,629
Shares, Exercised	(313,827)	(454,053)	(100,779)
Shares, Forfeited	(168,615)	(192,387)	(61,151)
Shares, Outstanding	4,344,535	4,375,906	3,814,782
Weighted-Average Exercise Price, Outstanding	$ 5.63	$ 4.35	$ 2.73
Shares, Exercisable	3,100,758
Weighted-Average Exercise Price, Granted	$ 8.79	$ 8.82	$ 8.77
Shares, Vested and expected to vest	4,257,819
Weighted-Average Exercise Price, Exercised	$ 3.21	$ 2.91	$ 2.11
Weighted-Average Exercise Price, Forfeited	$ 7.22	$ 6.78	$ 4.04
Weighted-Average Exercise Price, Outstanding	$ 6.07	$ 5.63	$ 4.35
Weighted-Average Exercise Price, Exercisable	$ 5.20
Weighted-Average Exercise Price, Vested and expected to vest	$ 6.02
Weighted-Average Grant-date Fair Value, Granted	$ 5.23	$ 5.24	$ 5.12
Total Intrinsic Value of options Exercised, Exercised	$ 2,087	$ 2,682	$ 670
Weighted-Average Remaining Contractual Term, Outstanding	6 years 9 months 22 days
Weighted-Average Remaining Contractual Term, Exercisable	6 years 2 months 1 day
Weighted-Average Remaining Contractual Term, Vested and expected to vest	6 years 9 months 11 days
Aggregate Intrinsic Value, Outstanding	16,918
Aggregate Intrinsic Value, Exercisable	14,774
Aggregate Intrinsic Value, Vested and expected to vest	$ 16,768

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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

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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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Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The total accumulated difference between fair values of underlying shares on dates of exercise and exercise price on options which were exercised (or share units converted) into shares during the reporting period under the plan.

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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.

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Gross number of share options (or share units) granted during the period.

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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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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 remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.

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