Note 5 - 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	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Foreign Currency Gain (Loss) [Member] | Call Option on Natural Gas Price [Member]
Amount of gain (loss) recognized	$ 32		$ (1,114)
Foreign Currency Gain (Loss) [Member] | Call and Put Options on Oil Price [Member]
Amount of gain (loss) recognized	230		(1,312)
Foreign Currency Gain (Loss) [Member] | Natural Gas Price Swap [Member]
Amount of gain (loss) recognized		369		767
Electricity Revenues [Member] | Currency Forward Contracts [Member]
Amount of gain (loss) recognized	689	869	1,154	(1,349)
Amount of gain (loss) recognized	$ 951	$ 1,238	$ (1,272)	$ (582)