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Note 12 - Retirement Plans (Details Textual) | 12 Months Ended
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Dec. 31, 2020 USD ($) | Dec. 31, 2019 USD ($) | Dec. 31, 2018 USD ($)
Deferred Compensation Plan Assets | $ 4,717,000 | $ 5,150,000 |
Retirement Plan Expense | $ 1,600,000 | $ 1,200,000 | $ 900,000
Defined Contribution Plan [Member] |  |  |
Company Matching Percentage on First Eight Percent of Employee Contributions | 50.00% |  |
Company Matching Percentage on First Six Percent of Employee Contributions |  | 50.00% | 50.00%
Employee Contribution Percentage for Which Company Will Match at Fifty Percent | 8.00% | 6.00% | 6.00%
Defined Contribution Plan Number of Investment Options | 23 |  |
Pension Plan [Member] |  |  |
Number of Non-contributory Defined Benefit Plans | 2 |  |
Liability, Defined Benefit Plan, Total | $ 1,600,000 | $ 1,600,000 |
Accumulated Other Comprehensive Income (Loss), Unrecognized Net Actuarial Losses, Net of Tax | 1,800,000 | 1,800,000 |
Defined Benefit Plan, Accumulated Benefit Obligation | 6,500,000 | 6,400,000 |
Defined Benefit Plan, Plan Assets, Amount, Ending Balance | 4,900,000 | 4,800,000 |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total | $ 0 | $ 0 | $ 0
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate | 2.04% | 2.83% |
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets | 7.00% | 7.50% |
Non-qualified Retirement Savings Plan [Member] |  |  |
Company Matching Percentage on First Ten Thousand Dollar Employee Contributions | 50.00% |  |
Officer Contribution for Which Company Will Match at Fifty Percent | $ 10,000 |  |
Select Employee Contribution for Which Company Will Match at Fifty Percent | 5,000 |  |
Non-qualified Retirement Savings Plan [Member] | Other Long-term Liabilities [Member] |  |  |
Deferred Compensation Liability, Classified, Noncurrent, Total | 4,700,000 | $ 5,200,000 |
Non-qualified Retirement Savings Plan [Member] | Other Noncurrent Assets [Member] |  |  |
Deferred Compensation Plan Assets | $ 4,700,000 | $ 5,200,000 |

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