Note 8 - Benefit Plans - Pension Plans With Projected Benefit Obligation in Excess of Plan Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Projected benefit obligation	$ 33,115	$ 28,470
Fair value of plan assets	(18,754)	(19,939)
Defined Benefit Plan, Pension Plans with Accumulated Benefit Obligations in Excess of Plan Assets, Funded Status	14,361	8,531
Pension Plan [Member]
Projected benefit obligation	18,778	18,114
Fair value of plan assets	(18,754)	(19,939)
Defined Benefit Plan, Pension Plans with Accumulated Benefit Obligations in Excess of Plan Assets, Funded Status	24	(1,825)
Supplemental Employee Retirement Plan [Member]
Projected benefit obligation	14,337	10,356
Fair value of plan assets	0	0
Defined Benefit Plan, Pension Plans with Accumulated Benefit Obligations in Excess of Plan Assets, Funded Status	$ 14,337	$ 10,356