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Note 12 - Retirement Plans (Details Textual) | 12 Months Ended
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Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($)
Company Matching Percentage on First Six Percent of Employee Contributions | 50.00% |  |
Employee Contribution Percentage for Which Company Will Match at Fifty Percent | 6.00% |  |
Defined Contribution Plan Number of Investment Options | 24 |  |
Number of Non-contributory Defined Benefit Plans | 2 |  |
Liability, Defined Benefit Plan | $ 1,700,000 | $ 1,900,000 |
Accumulated Other Comprehensive Income (Loss), Unrecognized Net Actuarial Losses, Net of Tax | 1,400,000 | 1,500,000 |
Defined Benefit Plan, Accumulated Benefit Obligation | 6,600,000 | 6,500,000 |
Defined Benefit Plan, Fair Value of Plan Assets | 4,900,000 | 4,600,000 |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) | $ 0 | $ 400,000 | $ 400,000
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate | 3.36% | 3.74% |
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets | 7.50% | 7.50% |
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 |  |
Retirement Target Benefit Plan, Percentage of Final Base Pay after 35-year Career | 35.00% |  |
Retirement Target Benefit Plan, Percentage of Final Base Pay per Year of Service | 1.00% |  |
Non-qualified Retirement Savings Plan Actuarial Yearly Asset Growth Percentage Assumption | 8.00% |  |
Deferred Compensation Liability, Current and Noncurrent | $ 6,200,000 | $ 6,200,000 |
Retirement Plan Expense | $ 900,000 | $ 1,400,000 | 1,500,000
Income (Loss) From Operations of Discontinued Operations [Member] |  |  |
Retirement Plan Expense |  |  | $ 100,000

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