Summary of Restricted Stock Activity (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
Jan. 31, 2012 Year	Jan. 31, 2011 Year
Restricted stock Units
Beginning Balance	2,131	226
Granted	2,236	1,990
Vested	(634)	(58)
Cancelled	(137)	(27)
Ending Balance	3,596	2,131
Weighted Average Grant Date Fair Value
Beginning Balance	$ 9.61	$ 9.46
Granted	$ 10.91	$ 9.61
Vested	$ 9.31	$ 9.56
Cancelled	$ 10.46	$ 8.52
Ending Balance	$ 10.71	$ 9.61
Weighted Average Remaining Contractual Term (Years)
Beginning Balance	1.72	2.26
Ending Balance	1.77	1.72
Aggregate intrinsic value
Beginning Balance	$ 27,130	$ 1,816
Ending Balance	$ 49,881	$ 27,130

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The total dollar difference between fair values of the underlying shares reserved for issuance and exercise prices pertaining to equity-based payment awards other than options outstanding under the plan as of the balance sheet date.

+ References

No definition available.

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- Definition

The weighted average remaining contractual term for outstanding equity instruments other than options.

+ References

No definition available.

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- Definition

The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

+ References

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- Definition

The weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect during the reporting period as a result of the occurrence of a terminating event specified in the contractual agreement of the plan.

+ References

+ Details

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- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

+ Details

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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A240

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- Definition

The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

+ References

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-Publisher FASB

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- Definition

The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A240

-Subparagraph b(2)(a)

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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