Earnings Per Share - Computation of Basic and Diluted Net Earnings (Loss) Per Share (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Numerator:
Net income (loss)	$ 10,789us-gaap_NetIncomeLoss	$ 10,854us-gaap_NetIncomeLoss
Denominator:
Denominator for basic earnings per share – weighted average shares (in shares)	20,725	20,703
Effect of dilutive securities:
Employee stock options (in shares)	57	136
Denominator for diluted earnings per share - weighted average shares (in shares)	20,782	20,839

Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method.

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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

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Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period.

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