Stock Based Compensation - Schedule of Changes in Stock Units (Detail) - $ / shares	9 Months Ended
Sep. 30, 2021	Sep. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Balance at beginning of period	95,888	105,309
Grants	12,110	32,149
Vesting	(31,081)	(36,880)
Forfeited/expired	(1,389)	(239)
Balance at end of period	75,528	100,339
Balance at beginning of period	$ 29.89	$ 29.93
Weighted Average Grant Date Fair Value, Grants	49.58	28.55
Weighted Average Grant Date Fair Value, Vesting	28.42	30.20
Weighted Average Grant Date Fair Value, Forfeited/expired	32.76	29.70
Balance at end of period	$ 33.60	$ 29.39
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Balance at beginning of period	0
Grants	22,597
Vesting	0
Forfeited/expired	0
Balance at end of period	22,597
Balance at beginning of period	$ 0
Weighted Average Grant Date Fair Value, Grants	48.91
Weighted Average Grant Date Fair Value, Vesting	0
Weighted Average Grant Date Fair Value, Forfeited/expired	0
Balance at end of period	$ 48.91
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Balance at beginning of period	0
Grants	22,597
Vesting	0
Forfeited/expired	0
Balance at end of period	22,597
Balance at beginning of period	$ 0
Weighted Average Grant Date Fair Value, Grants	48.91
Weighted Average Grant Date Fair Value, Vesting	0
Weighted Average Grant Date Fair Value, Forfeited/expired	0
Balance at end of period	$ 48.91

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
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-SubTopic 10
-Section 50
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-Subparagraph (c)(1)(iv)(3)
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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.

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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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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.

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

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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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