Summary of Stock Option Activity Under Equity Compensation Plans (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2011 Year
Number of options
Options outstanding at December 31, 2010	253,893
Exercised	217,360
Options outstanding and exercisable at December 31, 2011	36,533
Weighted average exercise price
Options outstanding at December 31, 2010	$ 8.15
Exercised	$ 8.63
Options outstanding and exercisable at December 31, 2011	$ 5.32
Remaining contractual life
Remaining Contractual Life	1.2
Aggregate intrinsic value
Aggregate Intrinsic Value	$ 1,222

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The weighted average price at which option holders acquired shares when converting their stock options into shares under the plan during the reporting period.

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

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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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The weighted average price as of the beginning of the year at which grantees can acquire the shares reserved for issuance under the stock option plan.

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The weighted average period between the balance sheet date and expiration for all awards outstanding under the plan, which may be expressed in a decimal value for number of years.

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

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