Note 8 - Benefit Plans - Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Interest cost on projected benefit obligation	$ 863	$ 1,084
Service cost - benefits earned during the period	152	117
Pension Plan [Member]
Interest cost on projected benefit obligation	541	721	$ 675
Expected return on plan assets	(1,555)	(1,491)	(1,717)
Recognized actuarial loss	539	643	526
Settlement loss	413	1,110	0
Net periodic pension cost after settlements	(62)	983	(516)
Service cost - benefits earned during the period	0	0
Supplemental Employee Retirement Plan [Member]
Interest cost on projected benefit obligation	322	363	295
Recognized actuarial loss	695	616	606
Net periodic pension cost after settlements	1,169	1,096	1,009
Service cost - benefits earned during the period	$ 152	$ 117	$ 108