Note 5 - Defined Benefit Plan - Defined Benefit Plan Activity (Details) - Pension Plan [Member] - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Service cost	$ 361	$ 270
Interest cost	184	205
Expected return on plan assets	(555)	(420)
Amortization of prior service cost	(3)	(27)
Recognized net actuarial loss	208	177
Net periodic benefit cost	$ 195	$ 205