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Stock Plans - Summary of Stock Option Activity (Detail) - $ / shares	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, Shares	559,656	735,001	955,446
Exercised, Shares	(274,704)	(198,535)	(215,724)
Granted, Shares		23,285
Stock options forfeitures, Shares		(95)	(4,721)
Outstanding Ending balance, Shares	283,998	559,656	735,001
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Outstanding Beginning balance, Weighted Average Exercise Price (dollars per share)	$ 45.78	$ 43.79	$ 42.75
Exercised, Weighted Average Exercise Price (dollars per share)	45.31	38.16	39.25
Granted, Weighted Average Exercise Price (dollars per share)		43.54
Forfeited, Weighted Average Exercise Price (dollars per share)		49.19	44.50
Outstanding Ending balance, Weighted Average Exercise Price (dollars per share)	$ 46.23	$ 45.78	$ 43.79
Exercisable at end of period	281,593	552,682	638,673
Share-based Compensation Arrangement by Share-based Payment Award, Options, Expirations in Period	954
Share-based Compensation Arrangements by Share-based Payment Award, Options, Expirations in Period, Weighted Average Exercise Price	$ 42.00

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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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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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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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The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

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Net number of share options (or share units) granted during the period.

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

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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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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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