Note 6 - Defined Benefit Plan - Defined Benefit Plan Activity (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Service cost			$ 810	$ 600
Interest cost			615	663
Expected return on plan assets			(1,260)	(1,095)
Amortization of prior service cost			(81)	(81)
Recognized net actuarial loss			531	474
Net periodic benefit cost			$ 615	$ 561
Pension Plan [Member]
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