Note 8 - Benefit Plans (Details Textual) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Defined Benefit Plans Number of Plans	2
Defined Benefit Plans Retirement Age	65 years
Defined Benefit Plan, Funded (Unfunded) Status of Plan, Total	$ (8,531)	$ (7,145)
Other Assets [Member] | Nonqualified Plan [Member]
Cash Surrender Value of Life Insurance	4,300	2,900
Other Noncurrent Liabilities [Member] | Nonqualified Plan [Member]
Deferred Compensation Liability, Classified, Noncurrent, Total	4,100	2,900
Pension Plan [Member]
Defined Benefit Plan, Funded (Unfunded) Status of Plan, Total	1,800
Defined Benefit Plan, Expected Amortization, Next Fiscal Year, Total	(1,300)
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year	100
Supplemental Employee Retirement Plan [Member]
Defined Benefit Plan, Funded (Unfunded) Status of Plan, Total	10,400
Postretirement Life Insurance [Member]
Cash Surrender Value of Life Insurance	3,600	2,700
Postretirement Life Insurance [Member] | Life Insurance Contracts [Member]
Gain (Loss) on Investments, Total	$ 700	(300)	$ 300
401(K) Plan [Member}
Defined Contribution Plan, Employer Matching Contribution, Percent of Match	25.00%
Defined Contribution Plan, Employer Discretionary Contribution, Percent	3.00%
Defined Contribution Plan, Employer Discretionary Contribution Amount	$ 900	$ 800	$ 1,000