Earnings Per Share - Computation of Earnings Per Share (Detail) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Earnings Per Share [Abstract]
Net income	$ 23,061	$ 15,029	$ 45,787	$ 28,939
Average number of common shares outstanding	30,458	22,983	30,441	22,970
Effect of dilutive stock options and restricted stock	185	293	209	310
Average number of common shares outstanding used to calculate diluted earnings per share	30,643	23,276	30,650	23,280

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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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