Stock-Based Compensation Plans - Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock Options Outstanding, Beginning balance	305,452
Stock Options Outstanding, Granted	187,088	164,244	116,852
Stock Options Outstanding, Exercised	(25,047)
Stock Options Outstanding, Expired	(2,070)
Stock Options Outstanding, Ending balance	465,423	305,452
Stock Options Outstanding, Exercisable	133,098
Weighted-Average Exercise Price, Outstanding, Beginning balance	$ 170.15
Weighted-Average Exercise Price, Granted	173.04
Weighted-Average Exercise Price, Exercised	117.81
Weighted-Average Exercise Price, Expired	174.09
Weighted-Average Exercise Price, Outstanding, Ending balance	174.11	$ 170.15
Weighted-Average Exercise Price, Exercisable	$ 178.58
Weighted-Average Life (In Years), Outstanding, Ending balance	8 years 2 months 12 days
Weighted-Average Life (In Years), Exercisable	7 years 4 months 24 days
Aggregate Intrinsic Value, Outstanding, Ending balance	$ 38
Aggregate Intrinsic Value, Exercisable	$ 38

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

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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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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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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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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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