Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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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 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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Description of method used to estimate fair value of award under share-based payment arrangement.

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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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Rate of weighted-average expected volatility for award under share-based payment arrangement.

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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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Gross 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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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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Expected term of 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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Value, before forfeiture, of shares granted under share-based payment arrangement. Excludes employee stock ownership plan (ESOP).

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Stock Option Plan and Restricted Stock Plan - Additional Information (Detail) - USD ($)										3 Months Ended		6 Months Ended
	May 18, 2020	Apr. 28, 2020	Jan. 28, 2020	Oct. 22, 2019	Jun. 26, 2019	Apr. 23, 2019	Oct. 23, 2018	Apr. 24, 2018	Oct. 24, 2017	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value assumptions method used												Black-Scholes options pricing model
Risk-free interest rate												1.83%
Expected dividend yield												1.62%
Expected life												6 years 7 months 20 days
Expected volatility												26.69%
Weighted-average grant-date fair value of options granted					$ 7.31
Stock compensation expense										$ 349,000	$ 313,000	$ 689,000	$ 625,000
Granted, Shares			11,250		398,850
Granted the period exercise price			$ 34.55		$ 29.70
Restricted Stock [Member] \| Non-Employee Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted shares granted		21,560	434			21,714		21,420
Restricted shares value		$ 600,000	$ 15,000			$ 660,000		$ 540,000
Restricted Stock [Member] \| Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation expense										160,000	135,000	335,000	270,000
Restricted Stock [Member] \| Officers [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted shares vesting period	3 years		3 years	3 years	3 years		3 years
Restricted shares granted	7,176		2,979	22,188	23,428		52,042		28,382
Restricted shares value	$ 200,000		$ 103,000	$ 785,000	$ 695,000		$ 1,440,000		$ 655,000
Stock compensation expense										$ 322,000	$ 210,000	$ 597,000	$ 415,000
Restricted Stock [Member] \| Officers [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted shares vesting period									1 year
Restricted Stock [Member] \| Officers [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted shares vesting period									3 years