Summarizes Stock Option Activity (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options outstanding, beginning balance, shares	2,163,825	2,132,506	2,508,828
Granted, shares	160,000	609,642	198,343
Excercised, shares	(176,896)	(571,964)	(548,331)
Forfeited, shares	(17,000)	(6,359)	(26,334)
Stock options outstanding, ending balance, shares	2,129,929	2,163,825	2,132,506
Stock options outstanding, beginning balance, weighted average exercise price	$ 8.12	$ 6.34	$ 5.71
Stock options excercisable, shares	1,520,720	1,222,959	1,257,858
Granted, weighted average exercise price	$ 12.88	$ 12.31	$ 9.29
Excercised, weighted average exercise price	$ 4.46	$ 5.88	$ 4.46
Forfeited, weighted average exercise price	$ 4.05	$ 5.66	$ 9.26
Stock options outstanding, ending balance, weighted average exercise price	$ 8.82	$ 8.12	$ 6.34
Stock options excercisable, weighted average exercise price	$ 7.57	$ 7.23	$ 7.20
Stock options outstanding, weighted-average remaining contractual term	6 years 11 months 27 days	6 years 8 months 27 days	7 years 22 days
Stock options outstanding, weighted-average remaining contractual term	6 years 2 months 12 days	6 years 26 days	6 years 2 months 12 days
Stock options outstanding, aggregate intrinsic value	$ 5,640	$ 15,408	$ 8,444
Stock options outstanding, aggregate intrinsic value	$ 5,966	$ 9,831	$ 3,902

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

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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 can acquire the shares reserved for issuance on stock options awarded.

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