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Note 1 - Summary of Significant Accounting Policies (Details Textual) - USD ($) $ in Thousands | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Jan. 01, 2019 | Dec. 31, 2015
Restricted Cash and Cash Equivalents, Noncurrent, Total | $ 1,025 | $ 1,032 |  |  |
Capitalized Drilling Costs | 11,600 | 9,900 | $ 6,800 |  |
Foreign Currency Transaction Gain (Loss), Realized | 10,310 | (9,680) | (2,737) |  |
Revenue from Contract with Customer, Including Assessed Tax | 567,137 | 577,775 | 645,957 |  |
Restricted Cash and Cash Equivalents, Total | 1,000 | 1,000 | 2,200 |  | $ 1,000
Subsequent Event [Member] |  |  |  |  |
Finance Lease, Right-of-Use Asset |  |  |  | $ 22,400 |
Finance Lease, Liability, Total |  |  |  | $ 22,400 |
Other Nonoperating Income (Expense) [Member] |  |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Except Service cost | 2,800 |  |  |  |
Accounting Standards Update 2014-09 [Member] | Pro Forma [Member] |  |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax |  | $ 1,900 | $ 1,300 |  |
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 2018-02 [Member] | AOCI Attributable to Parent [Member] |  |  |  |  |
Tax Cuts and Jobs Act of 2017 Reclassification From AOCI to Retained Earnings, Tax Effect | $ 12,600 |  |  |  |
Minimum [Member] |  |  |  |  |
Property, Plant and Equipment, Useful Life | 3 years |  |  |  |
Maximum [Member] |  |  |  |  |
Property, Plant and Equipment, Useful Life | 17 years |  |  |  |

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