Stock-Based Compensation Plan (Restricted Stock Activity) (Details) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock incentive plan, authorized common stock	500,000
Deferred Compensation Arrangements Unrecognized Compensation Cost Related To Unvested Restricted Stock	$ 255
Shares, Nonvested, beginning of period	18,488	16,701
Shares, Granted	21,828	22,488
Shares, Vested	(13,238)	(12,400)
Shares, Nonvested, end of period	27,078	26,789
Weighted Average Grant Date Fair Value, Nonvested, beginning of period	$ 30.39	$ 29.72
Weighted Average Grant Date Fair Value, Granted	28.83	30.69
Weighted Average Grant Date Fair Value, Vested	30.14	29.54
Weighted Average Grant Date Fair Value, Nonvested, end of period	$ 29.25	$ 30.62
Service Period [Member] \| Officer [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting service period of grants to executive officers	3 years
Preformence Measure [Mmeber] \| Executive Officer [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting service period of grants to executive officers	1 year

Deferred Compensation Arrangements Unrecognized Compensation Cost Related To Unvested Restricted Stock

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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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- Definition

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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- Definition

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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- Definition

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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- Definition

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

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- Definition

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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- Definition

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

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