Stock-Based Compensation Plans - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	9 Months Ended
Jan. 31, 2019	Sep. 30, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized compensation costs related to non-vested		$ 43.9
Weighted-average period over which cost is expected to be recognized		2 years 1 month 6 days
Employees [Member] \| Restricted Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of non-option equity instruments granted during the period		97,244
Weighted-average grant date fair value per share		$ 242.74
Employees [Member] \| Performance Based Share [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of non-option equity instruments granted during the period		16,716
Number of stock option equity instruments granted during the period		82,474
Weighted-average fair value each option granted		$ 38.83
Weighted-average grant date fair value per share		$ 224.13
President and Chief Operating Officer [Member] \| Performance Based Share [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of non-option equity instruments granted during the period	18,914
Grant date fair value	$ 5.8
Share-based compensation arrangement by share-based payment award award vesting date	Jan. 24, 2024
Fair value assumptions, Risk free interest rate	2.60%
Fair value assumptions, Dividend yield rate	0.80%
Fair value assumptions, Volatility rate	25.90%
Performance period	5 years
President and Chief Operating Officer [Member] \| Performance Based Share [Member] \| Range One [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of non-option equity instruments granted during the period	8,969
Weighted-average grant date fair value per share	$ 272.88
Percentage of fair market value of the common stock on the grant date	125.00%
President and Chief Operating Officer [Member] \| Performance Based Share [Member] \| Range Two [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of non-option equity instruments granted during the period	9,945
Weighted-average grant date fair value per share	$ 294.71
Percentage of fair market value of the common stock on the grant date	135.00%
President and Chief Operating Officer [Member] \| Incentive Stock Options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of stock option equity instruments granted during the period	76,868
Grant date fair value	$ 5.8
Share-based compensation arrangement by share-based payment award award vesting date	Jan. 24, 2024
Fair value assumptions, Risk free interest rate	2.60%
Fair value assumptions, Dividend yield rate	0.80%
Fair value assumptions, Volatility rate	25.80%
Share-based compensation arrangement by share-based payment award, options expiry date	Jul. 22, 2024
President and Chief Operating Officer [Member] \| Incentive Stock Options [Member] \| Range One [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of stock option equity instruments granted during the period	35,678
Weighted-average fair value each option granted	$ 272.88
Percentage of fair market value of the common stock on the grant date	125.00%
President and Chief Operating Officer [Member] \| Incentive Stock Options [Member] \| Range Two [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of stock option equity instruments granted during the period	41,189
Weighted-average fair value each option granted	$ 294.71
Percentage of fair market value of the common stock on the grant date	135.00%

Share-based compensation arrangement by share-based payment award award vesting date.

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- Definition

Share-based compensation arrangement by share-based payment award equity instruments other than options purchase price of common stock percent.

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Share-based compensation arrangement by share-based payment award period.

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Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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-Publisher FASB
-Name Accounting Standards Codification
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Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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Date the equity-based award expires, in CCYY-MM-DD format.

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- Definition

The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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- Definition

The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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The risk-free interest rate assumption that is used in valuing an option on its own shares.

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

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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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Purchase price of common stock expressed as a percentage of its fair value.

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