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Note 8 - Employee Benefit Plans (Details Textual) - USD ($) | 1 Months Ended | 12 Months Ended
--- | --- | ---
Jul. 31, 2017 | Apr. 30, 2017 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase |  |  |  | 2.00% | 2.00% |
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets |  |  |  | 6.62% | 7.20% |
Long-term Investments |  |  |  | $ 7,561,000 | $ 5,002,000 |
Defined Benefit Plan Assumed Long Term Rate Basis Spread |  |  |  | 1.00% |  |
Defined Benefit Plan, Fair Value of Plan Assets |  |  |  | $ 99,922,000 | 87,357,000 | $ 73,321,000
Defined Benefit Plan, Plan Assets, Contributions by Employer |  |  |  | $ 7,227,000 | 9,092,000 |
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 |  |  |  | $ 114,000 | 442,000 | 391,000
Capital Accumulation 401(K) Plan [Member] |  |  |  |  |  |
Defined Benefit Plan, Plan Assets, Contributions by Employer |  |  |  | $ 3,500,000 | 3,500,000 | $ 3,400,000
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 |  | $ 5,700,000 | $ 1,200,000 |  |  |
Pension Plan [Member] | Common Stock [Member] |  |  |  |  |  |
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year |  |  |  | $ 3,800,000 |  |
Supplemental Employee Retirement Plan [Member] |  |  |  |  |  |
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year |  |  |  | 500,000 |  |
Fair Value, Inputs, Level 3 [Member] |  |  |  |  |  |
Defined Benefit Plan, Fair Value of Plan Assets |  |  |  | 17,100,000 | 14,000,000 |
Company Stock [Member] |  |  |  |  |  |
Long-term Investments |  |  |  | 4,800,000 | 6,300,000 |
Real Estate [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |  |  |  |
Defined Benefit Plan, Fair Value of Plan Assets |  |  |  | 14,200,000 | 11,400,000 |
Collective Investment Funds [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |  |  |  |
Defined Benefit Plan, Fair Value of Plan Assets |  |  |  | $ 2,900,000 | $ 2,600,000 |
Assumed for 2016 Through 2018 [Member] |  |  |  |  |  |
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase | [1] |  |  |  | 0.00% |
Assumed for after 2018 [Member] |  |  |  |  |  |
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase | [1] |  |  | 2.00% | 2.00% |
[1] | 0% was assumed for years 2016 through 2018 and 2% was assumed thereafter.

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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 increase of compensation, used to determine benefit obligation of defined benefit plan. Plan includes, but is not limited to, pay-related defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(2) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + 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/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(3) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Amount of contribution received by defined benefit plan from employer which increases plan assets. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(5)(ii) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 6 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e2709-114920 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b)(3) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(5)(iv)(01) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Fair value of assets that have been segregated and restricted to provide pension or postretirement benefits. Assets include, but are not limited to, stocks, bonds, other investments, earnings from investments, and contributions by the employer and employees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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