Stock-Based Compensation - Summarized Information for the Plans (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding, Beginning Balance (in shares)	238,748
Exercised (in shares)	(117,324)
Expired (in shares)	(1,508)
Outstanding, Ending Balance (in shares)	119,916	238,748
Exercisable, Ending Balance (in shares)	119,916
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted Average Exercise Price, Outstanding, Beginning Balance (in dollars per share)	$ 23.30
Exercised (in dollars per share)	22.48
Expired (in dollars per share)	23.96
Weighted Average Exercise Price, Outstanding, Ending Balance (in dollars per share)	24.08	$ 23.30
Weighted Average Exercise Price, Exercisable (in dollars per share)	$ 24.08
Aggregate Intrinsic Value (thousands)	$ 1,969
Aggregate Intrinsic Value (thousands)	1,969
Aggregate intrinsic value of options exercised	$ 1,392	$ 425	$ 298

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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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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Number of options or other stock instruments for which the right to exercise has lapsed under the terms of the plan agreements.

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Number of options outstanding, including both vested and non-vested options.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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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 price at which option holders acquired shares when converting their stock options into shares.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options of the plan that expired.

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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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Number of share options (or share units) exercised during the current period.

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