Note 6 - Defined Benefit Plan - Defined Benefit Plan Activity (Details) - Pension Plan [Member] - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Service cost	$ 270	$ 200
Interest cost	205	221
Expected return on plan assets	(420)	(365)
Amortization of prior service cost	(27)	(27)
Recognized net actuarial loss	177	158
Net periodic benefit cost	$ 205	$ 187

Amount of gain (loss) recognized in net periodic benefit (cost) credit of defined benefit plan.

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Amount of expected return (loss) recognized in net periodic benefit (cost) credit, calculated based on expected long-term rate of return and market-related value of plan assets of defined benefit plan.

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Amount of cost recognized for passage of time related to defined benefit plan.

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Amount of net periodic benefit cost (credit) for defined benefit plan.

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Amount of cost for actuarial present value of benefits attributed to service rendered by employee for defined benefit plan.

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Amount, after tax, of reclassification adjustment from accumulated other comprehensive (income) loss for prior service cost (credit) of defined benefit plan.

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