Earnings Per Share (Detail) - shares	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Weighted average number of shares for calculation of basic EPS	36,103,520	36,742,168	36,364,380	36,713,294
Stock options, restricted stock awards and restricted stock units under equity incentive plans	344,642	62,908	105,379	117,919
Weighted average number of shares for calculation of diluted EPS	36,448,162	36,805,076	36,469,759	36,831,213
Stock options under equity incentive plans
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock that have been excluded from the diluted shares calculation	12,000	1,845,784	1,359,250	1,845,784

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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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 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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