Stock-Based Compensation - Summary Information for Stock Options (Detail)	12 Months Ended
Dec. 31, 2018 $ / shares shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Options, Outstanding at January 1, 2018 \| shares	301,958
Number of Options, Exercised \| shares	(89,557)
Number of Options, Terminated \| shares	(2,011)
Number of Options, Outstanding at December 31, 2018 \| shares	210,390
Number of Options, Exercisable at December 31, 2018 \| shares	197,241
Weighted-Average Exercise Price, Outstanding at January 1, 2018 \| $ / shares	$ 91.44
Weighted-Average Exercise Price, Exercised \| $ / shares	81.06
Weighted-Average Exercise Price, Terminated \| $ / shares	83.32
Weighted-Average Exercise Price, Outstanding at December 31, 2018 \| $ / shares	95.93
Weighted-Average Exercise Price, Exercisable at December 31, 2018 \| $ / shares	$ 92.02
Weighted-Average Remaining Contractual Life (years), Outstanding at December 31, 2018	3 years 7 months 6 days
Weighted-Average Remaining Contractual Life (years), Exercisable at December 31, 2018	3 years 4 months 24 days

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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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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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For presentations that combine terminations, 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 or that expired.

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Weighted average price of options that were either forfeited or expired.

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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 remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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

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