Note 8 - Benefit Plans (Details Textual) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Defined Benefit Plans Number of Plans	2
Defined Benefit Plans Retirement Age (Year)	65 years
Defined Benefit Plan, Funded (Unfunded) Status of Plan, Total	$ (14,361)	$ (8,531)
Other Assets [Member] | Nonqualified Plan [Member]
Cash Surrender Value of Life Insurance	5,000	4,300
Other Noncurrent Liabilities [Member] | Nonqualified Plan [Member]
Deferred Compensation Liability, Classified, Noncurrent, Total	4,800	4,100
Supplemental Employee Retirement Plan [Member]
Defined Benefit Plan, Funded (Unfunded) Status of Plan, Total	(14,337)	(10,356)
Defined Benefit Plan, Expected Amortization, Next Fiscal Year, Total	700
Pension Plan [Member]
Defined Benefit Plan, Funded (Unfunded) Status of Plan, Total	(24)	1,825
Defined Benefit Plan, Expected Amortization, Next Fiscal Year, Total	500
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year	0
Postretirement Life Insurance [Member]
Cash Surrender Value of Life Insurance	4,000	3,600
Postretirement Life Insurance [Member] | Life Insurance Contracts [Member]
Gain (Loss) on Investments, Total	$ 500	700	$ (300)
401(K) Plan [Member}
Defined Contribution Plan, Employer Matching Contribution, Percent of Match	25.00%
Defined Contribution Plan, Employer Discretionary Contribution Amount		$ 1,600	$ 1,000
Defined Contribution Plan, Increase (Decrease), Cost	$ (1,200)
Gain (loss) on Employer Matching Contribution, Amount	$ 300