Share-Based Compensation - Summary of RSUs Outstanding Under LTIP (Detail)	9 Months Ended
Sep. 30, 2021 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonvested as of January 1, 2021	199,563
Granted	63,593
Vested	(56,973)
Forfeited	0
Nonvested as of September 30, 2021	206,183
Nonvested as of January 1, 2021, Weighted-Average Grant-Date Fair Value \| $ / shares	$ 60.33
Weighted-Average Grant-Date Fair Value, Granted \| $ / shares	71.84
Weighted-Average Grant-Date Fair Value, Vested \| $ / shares	73.86
Weighted-Average Grant-Date Fair Value, Forfeited \| $ / shares	0.00
Nonvested as of September 30, 2021, Weighted-Average Grant-Date Fair Value \| $ / shares	$ 60.49
Performance and Service Required [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonvested as of January 1, 2021	183,777
Granted	51,308
Vested	(56,973)
Forfeited	0
Nonvested as of September 30, 2021	178,112
Service Required [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonvested as of January 1, 2021	15,786
Granted	12,285
Vested	0
Forfeited	0
Nonvested as of September 30, 2021	28,071

The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(3)
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- Definition

Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

+ References

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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).

+ References

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-Publisher FASB
-Name Accounting Standards Codification
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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).

+ References

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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

+ References

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Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options.

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-Publisher FASB
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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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-Publisher FASB
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The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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- Definition

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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No definition available.

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