Note 7 - Fair Value of Financial Instruments - Amounts of Gain (Loss) Recognized in Condensed Consolidated Statements on Derivative Instruments Not Designated as Hedges (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Amount of gain (loss) recognized	$ 2,556	$ 7,411	$ 5,268
Foreign Currency Gain (Loss) [Member] | Put Options on Natural Gas Price [Member]
Amount of gain (loss) recognized	0	0	(350)
Foreign Currency Gain (Loss) [Member] | Contingent Considerations [Member]
Amount of gain (loss) recognized	0	170	(129)
Foreign Currency Gain (Loss) [Member] | Currency Forward Contracts [Member]
Amount of gain (loss) recognized	2,556	(3,081)	3,699
General and Administrative Expense [Member] | Currency Forward Contracts [Member]
Amount of gain (loss) recognized	$ 0	$ 10,322	$ 2,048