Note 13 - Employee Benefit Plans (Details Textual) $ in Thousands	12 Months Ended
Dec. 31, 2019 USD ($) shares	Dec. 31, 2018 USD ($) shares	Dec. 31, 2017 USD ($) shares
Deferred Compensation Arrangement with Individual, Recorded Liability	$ 0	$ 0
Deferred Compensation Arrangement with Individual, Compensation Expense	0	0	$ 11
Stop-loss Insurance Liability for Individual Claims	175
Stop-loss Insurance Liability for Aggregate Claims	4,600
Other Postretirement Benefits Cost (Reversal of Cost)	$ 3,970	$ 3,720	$ 3,500
Common Stock, Shares Held in Employee Trust, Shares \| shares	346,833	366,969	387,935
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross \| shares	0	0
Share-based Payment Arrangement, Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value	$ 150	$ 423	$ 84
Share-based Payment Arrangement, Nonvested Award, Option, Cost Not yet Recognized, Amount	$ 10
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition	98 days
Restricted Stock [Member]
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition	1 year 328 days
Share-based Payment Arrangement, Nonvested Award, Excluding Option, Cost Not yet Recognized, Amount	$ 1,230
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 \| shares	600,000
Share-based Compensation Arrangement By Share-based Payment Award, Maximum Exercise Period	10 years
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	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	$ 1,100	$ 1,060	$ 1,180

Represents the employee contribution age for defined benefit plan.

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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.

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Amount of stop-loss insurance coverage for individual claims.

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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

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

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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.

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- Definition

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

+ References

No definition available.

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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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- 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.

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- Definition

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

+ References

No definition available.

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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.

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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.

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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.

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

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No definition available.

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

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