Stock Based Compensation - Additional Information (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Schedule Of Stock Option Activity [Line Items]
Share-based compensation expense	$ 2,595	$ 2,239	$ 1,788
Compensation expense related with stock options	1,274us-gaap_StockOptionPlanExpense	1,437us-gaap_StockOptionPlanExpense	1,093us-gaap_StockOptionPlanExpense
Compensation expense for stock awards	1,321us-gaap_RestrictedStockExpense	802us-gaap_RestrictedStockExpense	695us-gaap_RestrictedStockExpense
Maximum number of shares authorized to issued as options	1,131
Term life of options	10 years
Vesting period of stock issue	3 years	3 years	3 years
Number of options granted	108	354	285
Weighted average grant date fair value of the options granted	$ 9.48	$ 5.17	$ 4.27
Unrecognized compensation costs to be recognized for stock options	778
Unrecognized compensation costs to be recognized for restricted stocks	1,511
Unrecognized compensation costs, period for recognition	2 years
Cash proceeds from the exercise of options	1,671	4,013	22
Total intrinsic value of options exercised	$ 1,956	$ 1,416	$ 107
Common stock issued	114	90	78
Weighted average grant date fair value Per Share of the Stock Award	$ 20.15
Key Employees [Member]
Schedule Of Stock Option Activity [Line Items]
Vesting period of stock issue	3 years
Non-employee Directors [Member]
Schedule Of Stock Option Activity [Line Items]
Vesting period of stock issue	1 year

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Share based compensation arrangement by share based payment award maximum number of shares available.

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Share based compensation arrangement by share based payment award per share weighted average grant date fair value.

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Share based compensation arrangement by share based payment award terms of award.

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Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Unrecognized cost of unvested share-based awards, other than options, awarded to employees as compensation.

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Unrecognized cost of unvested options awarded to employees as compensation.

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The total cash inflow associated with the amount received from holders to acquire the entity's shares under incentive and share awards, including stock option exercises. This item inherently excludes any excess tax benefit, which the entity may have realized and reported separately.

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The noncash expense that represents the cost of restricted stock or unit distributed to employees as compensation.

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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Net 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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Number of share instruments newly issued under a share-based compensation plan.

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The noncash expense that accounts for the value of stock or unit options distributed to employees as compensation.

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