Summary of Stock Options Activity and Related Information (Detail) (USD $)	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Options
Beginning Balance	2,592,535	3,094,079	3,895,138
Granted	30,000	15,000	35,000
Canceled			(8,000)
Exercised	(911,527)	(499,700)	(828,059)
Expired/Forfeited		(16,844)
Ending Balance	1,711,008	2,592,535	3,094,079
Exercisable at December 31, 2011	1,711,008
Weighted-Average Exercise Price
Beginning Balance	$ 4.61	$ 4.48	$ 4.29
Granted	$ 20.44	$ 16.33	$ 13.77
Canceled			$ 16.96
Exercised	$ 3.61	$ 4.29	$ 3.84
Expired/Forfeited		$ 1.31
Ending Balance	$ 5.42	$ 4.61	$ 4.48
Exercisable at December 31, 2011	$ 5.42

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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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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 decrease in the number of shares that could be issued attributable to the lapse of rights to exercise previously issued stock options under the terms of the option agreements under the plan during the reporting period.

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The weighted average price at which grantees could have acquired the underlying shares with respect to stock options of the plan that lapsed during the reporting period.

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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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The weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated during the reporting period due to noncompliance with plan terms during the reporting period.

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

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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 stock options awarded under the plan during the reporting period.

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

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