Deferred compensation arrangement with individual compensation expense (income).

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Share based compensation number of deferrals.

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

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- Definition

Aggregate number of common shares reserved for future issuance.

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- Definition

Number of common stock held in a trust that has been set up specifically to accumulate stock for the sole purpose of distribution to participating employees but not yet earned.

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- Definition

Amount of deferred tax expense from write-off of the deferred tax asset related to deductible stock options at exercise.

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

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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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- Definition

Amount of cost to be recognized for nonvested award under share-based payment arrangement. Excludes share and unit options.

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- Definition

Amount of cost to be recognized for option under share-based payment arrangement.

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- Definition

Amount of cash inflow from realized tax benefit related to deductible compensation cost reported on the entity's tax return for equity instruments in excess of the compensation cost for those instruments recognized for financial reporting purposes.

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Amount of cash inflow from exercise of option under share-based payment arrangement.

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- Definition

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

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- Definition

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

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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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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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- Definition

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

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No definition available.

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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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Percentage of vesting of award under share-based payment arrangement.

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Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Number of share options (or share units) exercised during the current period.

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Value of forfeited shares issued under share-based payment arrangement. Excludes employee stock ownership plan (ESOP).

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Share-Based Compensation - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2020 USD ($) Deferral $ / shares shares	Dec. 31, 2019 USD ($) shares	Dec. 31, 2018 USD ($) shares	May 10, 2016 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted shares granted under incentive plan	81,086
Forfeiture of restricted stock based unit	13,814
Deferred shares and held by the rabbi trust	265,508	267,641
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common shares reserved for awards	800,000
Long Term Incentive Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common shares reserved for awards	100,000
Time-Based RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expenses \| $	$ 400,000	$ 500,000	$ 500,000
Compensation cost expected to be recognized over period \| $	$ 5,000,000
Weighted-average period	1 year 8 months 12 days
Time-Based RSUs [Member] \| Former Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Forfeiture of restricted stock based unit	2,763
Performance-Based RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average period	1 year 8 months 12 days
Performance-based compensation expense (income) \| $	$ 3,500,000	3,900,000	3,700,000
Remaining compensation expense \| $	$ 3,600,000
Performance-Based RSUs [Member] \| Former Officer [Member] \| Grant 2020, 2019 and 2018 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Forfeiture of restricted stock based unit	11,051
Service and Performance-based RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Excess tax benefits from restricted share awards \| $	$ 400,000	$ 500,000	$ 200,000
Long Term Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common shares reserved for awards	900,000
2016 Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common shares reserved for awards				1,000,000
Incentive plan expiry date	May 10, 2026
2016 Incentive Plan [Member] \| Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common shares reserved for awards				900,000
Restricted shares granted under incentive plan	316,685
2016 Incentive Plan [Member] \| Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common shares reserved for awards				100,000
Granted, Number of Shares	40,500
Deferred Compensation Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of deferrals \| Deferral	2
Long Term Incentive Plan and 2016 Incentive Plan [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option issued under plan vest and expire	5 years
Long Term Incentive Plan and 2016 Incentive Plan [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option issued under plan vest and expire	10 years
Long Term Incentive Plan and 2016 Incentive Plan [Member] \| After One Year [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option awards vesting percentage	50.00%
Long Term Incentive Plan and 2016 Incentive Plan [Member] \| After Two Years [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option awards vesting percentage	75.00%
Long Term Incentive Plan and 2016 Incentive Plan [Member] \| After Three Years [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option awards vesting percentage	100.00%
Long Term Incentive Plan Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted, Number of Shares	25,500	5,000	5,000
Compensation expenses \| $	$ 100,000
Weighted-average period	2 years 2 months 12 days
Estimated Forfeitures \| $	$ 0
Weighted average grant date fair value options granted \| $ / shares	$ 48.13
Exercised, Number of Shares	5,050	4,000	3,500
Total intrinsic value of stock options \| $		$ 100,000	$ 100,000
Cash received for the exercise of stock options \| $	$ 200,000	200,000
Expected compensation cost related to unvested awards not yet recognized \| $	300,000
Long Term Incentive Plan Stock Option [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expenses \| $		100,000	100,000
Total intrinsic value of stock options \| $	100,000
Excess tax benefits \| $	$ 100,000	$ 100,000	$ 100,000