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Employee Benefit Plans - Summary of Restricted Shares Issued, Vested and Forfeited (Detail)	12 Months Ended
	Dec. 31, 2021 Employee shares	Dec. 31, 2020 Employee shares	Dec. 31, 2019 Employee shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock awards, shares issued	48,750	37,382	38,100
Restricted Stock Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock awards, shares issued	48,750	37,382	38,100
Restricted shares vested	18,845	23,491	26,070
Restricted shares awarded due to retirement	4,425	10,890	14,300
Restricted shares awarded for other		1,050
Restricted shares forfeited	2,575	2,175	3,220
Restricted shares issued | Employee	96	92	94
Restricted shares vested | Employee	50	58	63
Restricted shares awarded due to retirement | Employee	7	8	3
Restricted shares awarded for other | Employee		1
Restricted shares forfeited | Employee	4	5	4

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Number of awards granted to one employee for other.

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Share based compensation arrangement by share based payment award equity instruments other than options vested excludes shares awarded due to retirement.

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Share based compensation arrangement by share based payment award number of employee share awarded due to other.

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Share Based Compensation Arrangement by share based payment award number of employee share awarded due to retirement.

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Share based compensation arrangement by share based payment award number of employee shares forfeited.

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Share based compensation arrangement by share based payment award number of employees.

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(3)
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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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Total number of shares issued during the period, including shares forfeited, as a result of Restricted Stock Awards.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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