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Note 8 - Employee Benefit Plans - Fair Value Measurements (Details) - USD ($) $ in Thousands | Dec. 31, 2017 | Dec. 31, 2016
--- | --- | ---
Fair value, plan assets |  | $ 23,428 | $ 17,038
Fair Value, Inputs, Level 1 [Member] |  |  |
Fair value, plan assets |  | 16,414 | 10,484
Fair Value, Inputs, Level 2 [Member] |  |  |
Fair value, plan assets |  | 7,014 | 6,554
Fair Value, Inputs, Level 3 [Member] |  |  |
Fair value, plan assets |  | 0 | 0
Cash [Member] |  |  |
Fair value, plan assets |  | 4,454 | 207
Cash [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |
Fair value, plan assets |  | 4,454 | 207
Cash [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |
Fair value, plan assets |  | 0 | 0
Cash [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |
Fair value, plan assets |  | 0 | 0
Equity Securities US Companies [Member] |  |  |
Fair value, plan assets |  | 9,892 | 9,195
Equity Securities US Companies [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |
Fair value, plan assets |  | 9,892 | 9,195
Equity Securities US Companies [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |
Fair value, plan assets |  | 0 | 0
Equity Securities US Companies [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |
Fair value, plan assets |  | 0 | 0
Equity Securities International Companies [Member] |  |  |
Fair value, plan assets |  | 106 | 116
Equity Securities International Companies [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |
Fair value, plan assets |  | 106 | 116
Equity Securities International Companies [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |
Fair value, plan assets |  | 0 | 0
Equity Securities International Companies [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |
Fair value, plan assets |  | 0 | 0
Equity Funds [Member] |  |  |
Fair value, plan assets | [1] | 1,962 | 966
Equity Funds [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |
Fair value, plan assets | [1] | 1,962 | 966
Equity Funds [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |
Fair value, plan assets | [1] | 0 | 0
Equity Funds [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |
Fair value, plan assets | [1] | 0 | 0
US Government Corporations and Agencies Securities [Member] |  |  |
Fair value, plan assets |  | 51 | 53
US Government Corporations and Agencies Securities [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |
Fair value, plan assets |  | 0 | 0
US Government Corporations and Agencies Securities [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |
Fair value, plan assets |  | 51 | 53
US Government Corporations and Agencies Securities [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |
Fair value, plan assets |  | 0 | 0
US States and Political Subdivisions Debt Securities [Member] |  |  |
Fair value, plan assets |  | 231 | 230
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |
Fair value, plan assets |  | 0 | 0
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |
Fair value, plan assets |  | 231 | 230
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |
Fair value, plan assets |  | 0 | 0
Corporate Debt Securities [Member] | External Credit Rating, Investment Grade [Member] |  |  |
Fair value, plan assets | [2] | 6,732 | 6,271
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member] | External Credit Rating, Investment Grade [Member] |  |  |
Fair value, plan assets | [2] | 0 | 0
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member] | External Credit Rating, Investment Grade [Member] |  |  |
Fair value, plan assets | [2] | 6,732 | 6,271
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member] | External Credit Rating, Investment Grade [Member] |  |  |
Fair value, plan assets | [2] | $ 0 | $ 0
[1] | This category comprises actively managed equity funds invested in large-cap and mid-cap U.S. companies.
[2] | This category represents investment grade bonds of U.S. issuers from diverse industries.

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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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