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Note 8 - Employee Benefit Plans - Benefit Obligation and Prepaid Benefit Costs Assumptions (Details) | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016
Discount rate: net periodic pension cost |  | 4.14% | 4.45%
Discount rate: projected benefit obligation |  | 3.83% | 4.14%
Expected rate of return on plan assets |  | 6.62% | 7.20%
Rate of compensation increase: net periodic pension cost |  | 2.00% | 2.00%
Assumed for after 2018 [Member] |  |  |
Rate of compensation increase: net periodic pension cost | [1] | 2.00% | 2.00%
Assumed for 2016 Through 2018 [Member] |  |  |
Rate of compensation increase: net periodic pension cost | [1] |  | 0.00%
[1] | 0% was assumed for years 2016 through 2018 and 2% was assumed thereafter.

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- Definition Weighted average rate for present value of future retirement benefits cash flows, used to determine benefit obligation 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)(1) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + 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 for present value of future retirement benefits cash flows, 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)(1) -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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