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Note 8 - Employee Benefit Plans (Details Textual) - USD ($) | 1 Months Ended | 12 Months Ended
--- | --- | ---
Jul. 31, 2016 | Feb. 29, 2016 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase |  |  |  |  | 2.00% |  |
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets |  |  |  | 6.80% | 7.20% |  |
Long-term Investments |  |  |  | $ 5,002,000 | $ 1,515,000 |  |
Defined Benefit Plan Assumed Long Term Rate Basis Spread |  |  |  | 1.00% |  |  |
Defined Benefit Plan, Fair Value of Plan Assets |  |  |  | $ 87,357,000 | 73,321,000 |  | $ 74,551,000
Defined Benefit Plan, Contributions by Employer |  |  |  | $ 9,092,000 | 5,460,000 |  |
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 Benefit Plan Months of Services Required for Eligibility |  |  |  | 180 days |  |  |
Defined Contribution Plan, Employer Discretionary Contribution Amount |  |  |  | $ 442,000 | 391,000 |  | 292,000
Capital Accumulation 401(K) Plan [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Contributions by Employer |  |  |  | $ 3,500,000 | 3,400,000 |  | $ 3,200,000
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, Contributions by Employer |  | $ 2,600,000 |  |  |  |  |
Pension Plan [Member] | Common Stock [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Contributions by Employer | $ 6,100,000 |  |  |  |  |  |
Fair Value, Inputs, Level 3 [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Fair Value of Plan Assets |  |  |  | $ 14,000,000 | 19,000,000 |  |
Company Stock [Member] |  |  |  |  |  |  |
Long-term Investments |  |  |  | 6,300,000 | 4,300,000 |  |
Real Estate [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Fair Value of Plan Assets |  |  |  | 11,400,000 | 13,200,000 |  |
Collective Investment Funds [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Fair Value of Plan Assets |  |  |  | $ 2,600,000 | $ 5,800,000 |  |
Assumed for 2016 Through 2018 [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase |  |  |  | 0.00% | 0.00% | [1] |
Assumed for after 2018 [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase |  |  |  | 2.00% | 2.00% | [1] |
Scenario, Forecast [Member] | Common Stock [Member] |  |  |  |  |  |  |
Defined Benefit Plans, Estimated Future Employer Contributions in Current Fiscal Year |  |  | $ 4,000,000 |  |  |  |
Scenario, Forecast [Member] | Unfunded Supplemental Executive Retirement Plan [Member] |  |  |  |  |  |  |
Defined Benefit Plans, Estimated Future Employer Contributions in Current Fiscal Year |  |  | $ 400,000 |  |  |  |
[1] | 0% was assumed for years 2016 through 2018 and 2% was assumed thereafter.

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- Definition Expected rate of compensation increases (for pay-related plans). + 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=65897934&loc=d3e1928-114920 + Details
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- Definition An assumption as to the rate of return on plan assets reflecting the average rate of earnings expected on the funds invested or to be invested to provide for the benefits included in the benefit obligation. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Expected Long-Term Rate of Return on Plan Assets -URI http://asc.fasb.org/extlink&oid=6512046 Reference 2: 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=65897934&loc=d3e1928-114920 + Details
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- Definition Amount of contributions made by the employer to defined benefit plans. + 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=65897934&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 60 -Section 35 -Paragraph 123 -Subparagraph B -URI http://asc.fasb.org/extlink&oid=64937487&loc=d3e36068-114959 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 30 -Section 35 -Paragraph 63 -Subparagraph B -URI http://asc.fasb.org/extlink&oid=64937038&loc=d3e12551-114930 Reference 4: 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=65897934&loc=d3e1928-114920 Reference 5: 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=65897934&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 30 -Section 35 -Paragraph 50 -URI http://asc.fasb.org/extlink&oid=64937038&loc=d3e12355-114930 Reference 2: 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=65897934&loc=d3e1928-114920 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Plan Assets -URI http://asc.fasb.org/extlink&oid=6749337 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Plan Assets -URI http://asc.fasb.org/extlink&oid=6520858 + Details
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