Common Stock, Dividends, Per Share, Declared, Increase Authorized

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Pre tax compensation expense related to director fees, annual retainers, and deferred compensation amortization.

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Weighted average purchase price of capital shares purchased through an employee stock purchase plan.

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Number of Stock Benefit Plans

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Quarterly Installment of Annual Cash Retainer

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Quarterly Installment Of Annual Cash Retainer, Percentage

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Quarterly Installment Of Annual Cash Retainer, Percentage Change

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Share-based Compensation Arrangement by Share-based Payment Award, Contractual Term of Award

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Share-Based Compensation Arrangement By Share-Based Payment Award, Equity Instruments Other Than Options, Granted In Period, Fair Value

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Share Based Compensation Arrangement By Share Based Payment Award, Options, Aggregate Grant Date Fair Value

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Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other Than Options, Grants in Period, Aggregate Grant Date Market Value

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

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Aggregate dividends paid during the period for each share of common stock outstanding.

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Aggregate dividends declared during the period for each share of common stock outstanding.

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Face amount or stated value per share of common stock.

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The maximum number of common shares permitted to be issued by an entity's charter and bylaws.

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Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury.

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Amount of paid and unpaid common stock dividends declared with the form of settlement in cash.

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

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Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

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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 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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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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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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Number of options or other stock instruments for which the right to exercise has lapsed under the terms of the plan agreements.

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The grant-date intrinsic value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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

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Amount by which current fair value of underlying stock exceeds exercise price of fully vested and expected to vest exercisable or convertible options. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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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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The excess of the fair value of the modified award over the fair value of the award immediately before the modification.

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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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Fair value of options vested. Excludes equity instruments other than options, for example, but not limited to, share units, stock appreciation rights, restricted stock.

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Purchase price of common stock expressed as a percentage of its fair value.

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Number of shares issued during the period as a result of an employee stock purchase plan.

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Stockholders' Equity Stockholders' Equity (Narrative) (Details)												3 Months Ended									12 Months Ended
	Dec. 31, 2020 USD ($) plan $ / shares shares	Oct. 30, 2020 $ / shares shares	Oct. 27, 2020 $ / shares	Aug. 31, 2020 $ / shares shares	Jun. 30, 2020 $ / shares shares	Jun. 26, 2020 shares	Jun. 25, 2020 $ / shares shares	May 19, 2020 $ / shares shares	Apr. 23, 2020 USD ($)	Apr. 19, 2020 USD ($)	Feb. 19, 2020 USD ($) shares	Dec. 31, 2020 USD ($) plan $ / shares shares	Sep. 30, 2020 USD ($) $ / shares	Jun. 30, 2020 USD ($) $ / shares	Mar. 31, 2020 USD ($) $ / shares	Dec. 31, 2019 USD ($) $ / shares shares	Sep. 30, 2019 USD ($) $ / shares	Jun. 30, 2019 USD ($) $ / shares	Mar. 31, 2019 USD ($) $ / shares	Mar. 31, 2017	Dec. 31, 2020 USD ($) plan $ / shares shares	Dec. 31, 2019 USD ($) $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares authorized (in shares) \| shares	80,000,000											80,000,000				80,000,000					80,000,000	80,000,000
Common stock, par value (in dollars per share) \| $ / shares	$ 0.01											$ 0.01				$ 0.01					$ 0.01	$ 0.01
Common stock, shares issued (in shares) \| shares	26,020,494											26,020,494				25,880,362					26,020,494	25,880,362
Treasury Stock, Shares \| shares	8,025,339											8,025,339				8,025,339					8,025,339	8,025,339
Stock options awarded (in shares) \| shares																					20,000	100,000	213,000
Grants, weighted average exercise price (in usd per share) \| $ / shares																					$ 18.02	$ 24.35	$ 25.43
Share-based Compensation Arrangement by Share-based Payment Award, Options, Expirations in Period \| shares																					146,000	298,000	165,000
Unrecognized share based compensation cost	$ 1,100,000											$ 1,100,000									$ 1,100,000
Unrecognized share based compensation, expected term (in years)																					10 months 24 days
Issuance of common stock from employee stock purchase plan (in shares) \| shares																					71,908	73,731	49,938
Weighted average purchase price of ESPP shares purchased during the period (in dollars per share) \| $ / shares																					$ 16.71	$ 13.18	$ 18.56
Director Compensation, Quarterly Installment Of Annual Cash Retainer									$ 35,000	$ 29,750	$ 35,000
Dividends declared per share (in dollars per share) \| $ / shares	$ 0.40											$ 0.1000	$ 0.0875	$ 0.0750	$ 0.0750						$ 0.3375	$ 0.3000	$ 0.3000
Dividends declared, common stock, amount												$ 1,797,000	$ 1,569,000	$ 1,343,000	$ 1,339,000	$ 1,337,000	$ 1,336,000	$ 1,365,000	$ 1,360,000
Common Stock, Dividends, Per Share, Cash Paid \| $ / shares																$ 0.0750	$ 0.0750	$ 0.0750	$ 0.0750
Number of Stock Benefit Plans \| plan	2											2									2
Quarterly Installment Of Annual Cash Retainer, Percentage Change										15.00%
Quarterly Installment Of Annual Cash Retainer, Percentage						100.00%
Common Stock, Dividends, Per Share, Declared, Increase Authorized \| $ / shares			$ 0.0125					$ 0.05
Good to Great Incentive Program [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options awarded (in shares) \| shares																					17,991	14,844	5,712
Total intrinsic value of options exercised																					$ 400,000	$ 300,000	$ 100,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Grant Date Intrinsic Value \| $ / shares																					$ 25.00	$ 19.92	$ 25.43
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Exercisable, Aggregate Intrinsic Value	$ 5,600,000											$ 5,600,000									$ 5,600,000
Contractual term of all options granted																					7 years
Stock options awarded (in shares) \| shares																					20,000	100,000	212,940
Grants, weighted average exercise price (in usd per share) \| $ / shares																					$ 18.02		$ 25.43
Stock option, contracted term																					10 years
Value of stock options granted																					$ 100,000	$ 600,000	$ 1,400,000
Total intrinsic value of options exercised																					500,000	1,200,000	3,900,000
Total fair value of stock options vested																					700,000	900,000	1,500,000
Share based compensation expense																					700,000	700,000	1,000,000.0
Unrecognized share based compensation cost	800,000											800,000									$ 800,000
Unrecognized share based compensation, expected term (in years)																					1 year 6 months 10 days
Incremental award vesting percentage																				20.00%
Employee Stock Option \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Contractual term of all options granted																					10 years
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation expense																					$ 400,000	300,000	200,000
Purchase price percentage of grant date price per share (as a percent)																					85.00%
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Cancellations ( in usd per share) \| $ / shares																					$ 0
Share based compensation expense																					$ 700,000	$ 800,000	$ 800,000
Cancellations (in shares) \| shares																					0
Awards (in shares) \| shares																					10,200
Awards ( in usd per share) \| $ / shares																					$ 25.00
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period (in years)																					3 years
Awards (in shares) \| shares																					10,200	25,550	86,260
Awards granted, aggregate grant date market value																					$ 300,000	$ 500,000	$ 2,200,000
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants, weighted average exercise price (in usd per share) \| $ / shares		$ 25.81		$ 22.14	$ 23.10		$ 18.02	$ 15.79
Cancellations ( in usd per share) \| $ / shares																					$ 9.69
Cancellations (in shares) \| shares						(33,538)
Unrecognized share based compensation cost	$ 5,000,000.0											$ 5,000,000.0									$ 5,000,000.0
Unrecognized share based compensation, expected term (in years)																					4 years
Awards (in shares) \| shares		6,987		6,987	2,795		13,974	368,921			237,500										399,664	306,623	113,320
Share-Based Compensation Arrangement By Share-Based Payment Award, Equity Instruments Other Than Options, Granted In Period, Fair Value											$ 2,800,000											$ 1,600,000	$ 2,900,000
Awards ( in usd per share) \| $ / shares																					$ 10.79
Share-based Goods and Nonemployee Services Transaction, Modification of Terms, Incremental Compensation Cost																					$ 1,700,000
Officers And Key Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Directors compensation expense																					900,000	200,000	4,400,000
Board of Directors
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Directors compensation expense																					$ 900,000	$ 500,000	$ 500,000
Director
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options awarded (in shares) \| shares																					30,883	7,458	7,403
Value of stock options granted																					$ 700,000	$ 200,000	$ 200,000
Cancellations ( in usd per share) \| $ / shares																					$ 21.16	$ 20.78	$ 20.52