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