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Note 9 - Employee Benefit Plans (Details Textual) - USD ($) | 1 Months Ended | 2 Months Ended | 12 Months Ended
--- | --- | --- | ---
Jan. 31, 2021 | Feb. 18, 2021 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets |  |  | 6.45% | 6.37% |
Defined Benefit Plan Assumed Long Term Rate Basis Spread |  |  | 1.00% |  |
Defined Benefit Plan, Plan Assets, Contributions by Employer |  |  | $ 23,731,000 | $ 4,095,000 |
Defined Contribution Plan, Employer Matching Contribution, Percent of Match |  |  | 55.00% |  |
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay |  |  | 5.00% |  |
Defined Contribution Plan, Employer Discretionary Contribution Amount |  |  | $ 10,000 | 10,000 | $ 4,000
Capital Accumulation 401(K) Plan [Member] |  |  |  |  |
Defined Benefit Plan, Plan Assets, Contributions by Employer |  |  | $ 4,600,000 | 3,900,000 | 3,700,000
Defined Contribution Plan, Employer Matching Contribution, Percent of Match |  |  | 100.00% |  |
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay |  |  | 6.00% |  |
Minimum [Member] |  |  |  |  |
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent |  |  | 2.00% |  |
Minimum [Member] | Capital Accumulation 401(K) Plan [Member] |  |  |  |  |
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent |  |  | 1.00% |  |
Maximum [Member] |  |  |  |  |
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent |  |  | 50.00% |  |
Maximum [Member] | Capital Accumulation 401(K) Plan [Member] |  |  |  |  |
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent |  |  | 50.00% |  |
Pension Plan [Member] |  |  |  |  |
Defined Benefit Plan, Plan Assets, Contributions by Employer |  |  | $ 16,000,000.0 |  |
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year |  |  | 6,000,000.0 |  |
Supplemental Employee Retirement Plan [Member] |  |  |  |  |
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year |  |  | 800,000 |  |
Defined Benefit Plan, Equity Securities, Common Stock [Member] |  |  |  |  |
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount |  |  | 17,200,000 | 14,700,000 |
Nonoperating Income (Expense) [Member] |  |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Except Service cost |  |  | $ 2,900,000 | $ 5,000,000.0 | $ 2,800,000
Subsequent Event [Member] |  |  |  |  |
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets |  | 6.40% |  |  |
Subsequent Event [Member] | Supplemental Employee Retirement Plan [Member] |  |  |  |  |
Defined Benefit Plan, Plan Assets, Contributions by Employer | $ 16,800,000 |  |  |  |

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- Definition Assumed long term rate basis spread for defined benefit plan. + References No definition available. + Details
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- Definition Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(3) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e2919-114920 + Details
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