Note 13 - Employee Benefit Plans (Details Textual) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Deferred Compensation Arrangement with Individual, Recorded Liability	$ 0	$ 0
Deferred Compensation Arrangement with Individual, Compensation Expense	0	0	$ 0
Stop-loss Insurance Liability for Individual Claims	200
Stop-loss Insurance Liability for Aggregate Claims	6,000
Other Postretirement Benefits Cost (Reversal of Cost)	$ 4,170	$ 3,970	$ 3,720
Common Stock, Shares Held in Employee Trust, Shares (in shares)	351,222	346,833	366,969
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares)	0	0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period (in shares)	(0)	8,459	24,186
Share-based Payment Arrangement, Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value		$ 150	$ 423
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Number of Shares, Ending Balance (in shares)	0
Share-based Payment Arrangement, Nonvested Award, Option, Cost Not yet Recognized, Amount	$ 0
Restricted Stock [Member]
Share-based Payment Arrangement, Nonvested Award, Excluding Option, Cost Not yet Recognized, Amount	$ 1,380
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)	1 year 9 months 29 days
2012 Omnibus Incentive Compensation Plan [Member] \| Share-based Payment Arrangement, Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant (in shares)	600,000
Share-based Compensation Arrangement By Share-based Payment Award, Maximum Exercise Period (Year)	10 years
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Year)	4 years
2012 Omnibus Incentive Compensation Plan [Member] \| Share-based Payment Arrangement, Option [Member] \| Share-based Payment Arrangement, Tranche One [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage	25.00%
Supplemental Employee Retirement Plan [Member]
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent	35.00%
Defined Benefit Plan, Employee Contribution, Age	62
Directors' Plan [Member]
Defined Benefit Plan, Employee Contribution, Age	70
Defined Contribution Plan, Maximum Employee Contribution as Percentage of Base Salary	100.00%
401 (k) Savings Plan [Member]
Defined Benefit Plan, Employer Matching Contributions	$ 1,510	$ 1,100	$ 1,060

Represents the employee contribution age for defined benefit plan.

No definition available.

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- Definition

Amount of employer matching contributions to the plan.

+ References

No definition available.

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- Definition

Represents the maximum percentage of base salary the employee contribution.

+ References

No definition available.

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- Definition

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

+ References

No definition available.

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- Definition

Amount of stop-loss insurance coverage for aggregate claims.

+ References

No definition available.

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- Definition

Amount of stop-loss insurance coverage for individual claims.

+ References

No definition available.

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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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 40
-Section 25
-Paragraph 12
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- Definition

The compensation expense recognized during the period pertaining to the deferred compensation arrangement.

+ References

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- Definition

The carrying amount of the liability as of the balance sheet date to an individual under a deferred compensation arrangement. This amount may be the result of periodic accruals made over the period of active employment, or reflect termination benefits resulting contractual terms or a death benefit.

+ References

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- Definition

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

+ References

No definition available.

+ Details

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- Definition

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.

+ References

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- Definition

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

+ References

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- Definition

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

+ References

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- Definition

Amount of cost (reversal of cost) for other postretirement benefits. Excludes pension benefits.

+ References

No definition available.

+ Details

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- Definition

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.

+ References

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- Definition

The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

+ References

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- Definition

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.

+ References

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- Definition

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

+ References

No definition available.

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- Definition

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

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- Definition

Number of non-vested options outstanding.

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- Definition

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

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