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Note 10 - Developments in Accounting Pronouncements (Details Textual) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | ---
Mar. 31, 2018 | Mar. 31, 2017 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Revenue from Contract with Customer, Including Assessed Tax | $ 139,709 | $ 142,544 |  |  |
Restricted Cash and Cash Equivalents, Total | 1,000 | 2,200 |  | $ 1,000 | $ 2,200
Cost of Goods Sold Before Depreciation, Depletion, and Amortization | 72,869 | 78,676 |  |  |
Other Nonoperating Income (Expense) [Member] |  |  |  |  |
Net Periodic Defined Benefits Expense (Reversal of Expense), Excluding Service Cost Component | 700 |  |  |  |
Scenario, Forecast [Member] | Other Nonoperating Income (Expense) [Member] |  |  |  |  |
Net Periodic Defined Benefits Expense (Reversal of Expense), Excluding Service Cost Component |  |  | $ 2,800 |  |
Accounting Standards Update 2014-09 [Member] | Pro Forma [Member] |  |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax |  | 140 |  |  |
Cost of Goods Sold Before Depreciation, Depletion, and Amortization |  | $ 140 |  |  |
Accounting Standards Update 2016-01 [Member] | AOCI Attributable to Parent [Member] |  |  |  |  |
Reclassification from Accumulated Other Comprehensive Income to Retained Earnings | 1,300 |  |  |  |
Accounting Standards Update 2016-01 [Member] | Retained Earnings [Member] |  |  |  |  |
Reclassification from Accumulated Other Comprehensive Income to Retained Earnings | $ (1,300) |  |  |  |

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