The aggregate number of shares of common stock that may be subject to awards granted in any calendar year.

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The aggregate amount of dividend equivalents charged against retained earnings when dividends were declared.

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The percentage Company Match of eligible executive compensation under the Supplemental plan before it is reduced by the amount of any contributions allocated to such executive under the Retirement Plan.

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Percentage Of Equity Instruments Other Than Options Vesting Per Year

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Restricted stock units shares issued upon conversion.

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Schedule of share based compensation arrangements by share based payment award options.

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Share based compensation arrangement by share based payment award equity instruments other than options vested.

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Share based compensation arrangement by share based payment award equity instruments other than options vested at specified date intrinsic value.

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Share-based compensation arrangement by share-based payment award, expiration month and year.

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Share based compensation arrangement by share based payment award vesting period on cumulative basis from date of grant.

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Value of specified shares of common stock equals each vested restricted stock unit on settlement date.

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

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Amount of payment to participant of defined benefit plan which decreases benefit obligation. For pension plan, payment includes, but is not limited to, pension benefits and death benefits. For other postretirement plan, payment includes, but is not limited to, prescription drug benefits, health care benefits, life insurance benefits, and legal, educational and advisory services.

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Amount of discretionary contributions made by an employer to a defined contribution plan.

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Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan.

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Maximum percentage of employee gross pay the employee may contribute to a defined contribution plan.

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

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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 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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Number of additional shares authorized for issuance under share-based payment arrangement.

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Number of shares authorized for issuance under share-based payment arrangement.

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

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Intrinsic value of nonvested award under share-based payment arrangement. Excludes share and unit options.

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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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Employee Benefit Plans - Additional Information (Detail) - USD ($)	1 Months Ended			12 Months Ended
	May 31, 2017	Feb. 28, 2013	Apr. 30, 2012	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Schedule Of Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items]
Grant awards	1,500,000			1,000,000
Maximum number of shares of common stock	200,000			100,000
Incentive compensation program expiration				2022-05
Fair value of grants recognition period				5 years
Additional grant awards	500,000
Vested of common stock				1
Issuance of common stock				1
Dividend equivalents charged against retained earnings when common stock dividends were declared				$ 997,000	$ 749,000	$ 542,000
Compensation expense				$ 2,468,000	1,777,000	1,350,000
Employer matching contribution percent				50.00%
Employee compensation				3.00%
Contributions, net of forfeitures				$ 327,000	$ 295,000	$ 282,000
Restricted Stock Units [Member]
Schedule Of Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items]
Restricted stock awarded				156,750	124,650	94,250
Termination of grant				10 years
RSUs vest starting period from date of grant				1 year
Annual rate of vest of total number of RSUs				20.00%
Number of outstanding RSUs				702,025	573,575	448,925	429,775
Number of vested RSUs				349,135	289,020	225,385	221,819
Restricted Stock Units [Member] \| 2012 Incentive Program [Member] \| Employees And Directors [Member]
Schedule Of Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items]
Restricted stock awarded		35,000
Restricted Stock Units [Member] \| 2004 Omnibus Incentive Compensation Plan [Member]
Schedule Of Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items]
Fair value of grants recognition period				5 years
Compensation expense				$ 2,447,000	$ 1,752,000	$ 1,328,000
Weighted average period				3 years
Number of outstanding RSUs				702,025
Number of vested RSUs				349,135
Intrinsic value of outstanding RSUs				$ 23,076,000
Intrinsic value of vested RSUs				11,476,000
Restricted Stock Units [Member] \| 2004 Incentive Plan [Member]
Schedule Of Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items]
Unrecognized compensation cost				$ 7,694,000
Supplemental Employee Retirement Plan [Member]
Schedule Of Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items]
Executive compensation				10.00%
Distribution from supplemental plan					$ 0
Supplemental Employee Retirement Plan [Member] \| Former Officers [Member]
Schedule Of Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items]
Distribution from supplemental plan				$ 30,000		$ 278,000
Tranche One [Member]
Schedule Of Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items]
Incentive compensation program vesting percentage				20.00%
Tranche One [Member] \| Restricted Stock Units [Member] \| 2012 Incentive Program [Member] \| Employees And Directors [Member]
Schedule Of Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items]
Incentive compensation program vesting percentage			20.00%
Tranche Two [Member] \| Restricted Stock Units [Member] \| 2012 Incentive Program [Member] \| Employees And Directors [Member]
Schedule Of Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items]
Incentive compensation program vesting percentage			20.00%
Tranche Three [Member] \| Restricted Stock Units [Member] \| 2012 Incentive Program [Member] \| Employees And Directors [Member]
Schedule Of Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items]
Incentive compensation program vesting percentage			20.00%
Tranche Four [Member] \| Restricted Stock Units [Member] \| 2012 Incentive Program [Member] \| Employees And Directors [Member]
Schedule Of Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items]
Incentive compensation program vesting percentage			20.00%
Tranche Five [Member] \| Restricted Stock Units [Member] \| 2012 Incentive Program [Member] \| Employees And Directors [Member]
Schedule Of Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items]
Incentive compensation program vesting percentage			20.00%