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Note 11 - Developments in Accounting Pronouncements (Details Textual) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | --- | ---
Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2018 | Sep. 30, 2017 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Revenue from Contract with Customer, Including Assessed Tax | $ 143,649 | $ 140,839 | $ 430,617 | $ 417,662 |  |  |
Restricted Cash and Cash Equivalents, Total | 1,000 | $ 1,100 | 1,000 | 1,100 |  | $ 1,000 | $ 2,200
Other Nonoperating Income (Expense) [Member] |  |  |  |  |  |  |
Net Periodic Defined Benefits Expense (Reversal of Expense), Excluding Service Cost Component | $ 700 |  | 2,100 |  |  |  |
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 |  |  |  | $ 1,200 |  |  |
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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- Definition Amount of cash and cash equivalents restricted as to withdrawal or usage. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(2)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(1)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=98513485&loc=SL98516268-108586 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(1)(a)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3044-108585 + Details
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