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
	Mar. 31, 2017	Mar. 31, 2016
Amount of gain (loss) recognized	$ 2,019	$ 1,689
Foreign Currency Gain (Loss) [Member] | Put Options on Natural Gas Price [Member]
Amount of gain (loss) recognized	(193)
Foreign Currency Gain (Loss) [Member] | Call Option on Natural Gas Price [Member]
Amount of gain (loss) recognized		518
Foreign Currency Gain (Loss) [Member] | Call and Put Options on Oil Price [Member]
Amount of gain (loss) recognized		(643)
Foreign Currency Gain (Loss) [Member] | Contingent Considerations [Member]
Amount of gain (loss) recognized	(50)
Foreign Currency Gain (Loss) [Member] | Currency Forward Contracts [Member]
Amount of gain (loss) recognized	$ 2,262	$ 1,814