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Note 8 - Employee Benefit Plans (Details Textual) - USD ($)
$ in Thousands
 3 Months Ended 12 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Dec. 31, 2019
Dec. 31, 2020
Pension Plan [Member]        
Defined Benefit Plan, Plan Assets, Contributions by Employer     $ 0  
Supplemental Employee Retirement Plan [Member]        
Defined Benefit Plan, Plan Assets, Contributions by Employer $ 400 $ 400    
Defined Benefit Plan, Expected Future Employer Contributions, Remainder of Fiscal Year 1,200      
Defined Benefit Plan, Benefit Obligation, Ending Balance $ 22,800     $ 22,800