Note 8 - Accrued Retirement Benefits - Net Periodic Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Interest cost	$ 408	$ 527	$ 1,225	$ 1,580
Expected return on plan assets	(489)	(480)	(1,483)	(1,446)
Amortization of net loss	206	211	617	634
Pension and other postretirement expenses	$ 125	$ 258	$ 359	$ 768