Represents the targeted percentage of equity used in adjusted return during the period.

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Represents the number of shares authorized for actual payment.

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Represents the number of trading days used to set the average beginning and ending share prices for the change in total shareholder value over the performance measurement period and to establish the grant-date fair value of the performance share awards.

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Represents the actual payout as a percent of target at the end of the performance measurement period.

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No definition available.

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Represents the percentage of target amount as a actual payment.

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Represents the period specified for average adjusted return, used to determine the achievement of a target.

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Represents the percentage of the market price of common shares at the end of each six-month purchase period at which eligible employees may purchase shares.

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No definition available.

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

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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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Discount rate from fair value on purchase date that participants pay for shares.

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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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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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Note 6 - Share-based Payments (Details Textual) - USD ($)						6 Months Ended	12 Months Ended				24 Months Ended	30 Months Ended	36 Months Ended		60 Months Ended
	Apr. 08, 2023	Dec. 17, 2019	Apr. 08, 2019	Feb. 13, 2019	Feb. 06, 2019	Dec. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2019	Jun. 30, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total						$ 3,500,000	$ 3,500,000
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition							1 year 10 months 24 days
Restricted Stock [Member] \| Director [Member]
Share-based Payment Arrangement, Expense							$ 776,000	$ 661,000	$ 658,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period			15,700				15,700	18,200	17,600
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value			$ 49.73				$ 49.73	$ 43.40	$ 37.75
Restricted Stock [Member] \| Director [Member] \| Share-based Payment Arrangement, Tranche One [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage			33.30%
Restricted Stock [Member] \| Director [Member] \| Share-based Payment Arrangement, Tranche Two [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage			33.30%
Restricted Stock [Member] \| Director [Member] \| Share-based Payment Arrangement, Tranche Three [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage			33.30%
Restricted Stock [Member] \| Employees [Member]
Share-based Payment Arrangement, Expense							$ 0	$ 16,000	$ 70,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period							0	0	0
Restricted Stock Units (RSUs) [Member] \| Employees [Member]
Share-based Payment Arrangement, Expense							$ 427,000	$ 351,000	$ 331,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period							13,270	14,780	10,995
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value							$ 44.45	$ 38.99	$ 33.28
Stock Performance Awards [Member] \| Executive Officer [Member]
Share-based Payment Arrangement, Expense							$ 3,597,000	$ 2,645,000	$ 2,007,000
Stock Performance Awards [Member] \| Executive Officer [Member] \| Performance Period 2017 To 2019 [Member]
Adjusted Return, Targeted Percentage of Equity							9.50%
Payout as a Percent of Target							120.19%
Stock Performance Awards [Member] \| Executive Officer [Member] \| Performance Period 2016 To 2018 [Member]
Adjusted Return, Targeted Percentage of Equity													10.00%
Payout as a Percent of Target													145.17%
Stock Performance Awards [Member] \| Executive Officer [Member] \| Performance Period 2015 To 2017 [Member]
Adjusted Return, Targeted Percentage of Equity														10.00%
Payout as a Percent of Target														136.00%
The 1999 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Discount from Market Price, Purchase Date										15.00%
Share-based Compensation Arrangements by Share-based Payment Award, Percentage of Market Price at Eligible Employees Granted Options to Purchase Shares						85.00%	100.00%				100.00%	15.00%
Share-based Payment Arrangement, Expense						$ 103,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized						1,400,000	1,400,000
The 1999 Stock Incentive Plan [Member] \| Restricted Stock [Member] \| Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period															0
The 2014 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized						1,900,000	1,900,000
The 2014 Stock Incentive Plan [Member] \| Restricted Stock [Member] \| Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period							13,270
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value							$ 44.45
The 2014 Stock Incentive Plan [Member] \| Restricted Stock [Member] \| Employees [Member] \| Share-based Payment Arrangement, Tranche One [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage	100.00%
The 2014 Stock Incentive Plan [Member] \| Restricted Stock [Member] \| Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period				15,600
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value				$ 49.6225
The 2014 Stock Incentive Plan [Member] \| Restricted Stock [Member] \| Executive Officer [Member] \| Share-based Payment Arrangement, Tranche One [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage					25.00%
The 2014 Stock Incentive Plan [Member] \| Restricted Stock [Member] \| Key Employee [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period		600
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value		$ 52.165
The 2014 Stock Incentive Plan [Member] \| Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period							4 years
The 2014 Stock Incentive Plan [Member] \| Stock Performance Awards [Member] \| Executive Officer [Member]
Period Specified for Average Adjusted Return							3 years
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized				55,600
Number of Trading Days				20 days
Number of Shares Authorized for Actual Payment				83,400
The 2014 Stock Incentive Plan [Member] \| Stock Performance Awards [Member] \| Executive Officer [Member] \| Minimum [Member]
Percentage of Target Amount as Actual Payment				0.00%
The 2014 Stock Incentive Plan [Member] \| Stock Performance Awards [Member] \| Executive Officer [Member] \| Maximum [Member]
Percentage of Target Amount as Actual Payment				150.00%
The 2014 Stock Incentive Plan [Member] \| Stock Performance Awards [Member] \| Executive Officer [Member] \| Share-based Payment Arrangement, Tranche Two [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized				27,800