Note 8 - 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, 2016	Dec. 31, 2015	Dec. 31, 2014
Call options on natural gas price	$ (3,942)	$ (48)	$ 775
Foreign Currency Gain (Loss) [Member] | Call Option on Natural Gas Price [Member]
Call options on natural gas price	(1,340)
Foreign Currency Gain (Loss) [Member] | Call and Put Options on Oil Price [Member]
Call options on natural gas price	(1,313)
Foreign Currency Gain (Loss) [Member] | Contingent Considerations [Member]
Call options on natural gas price	(1,527)
Foreign Currency Gain (Loss) [Member] | Currency Forward Contracts [Member]
Call options on natural gas price	238	(1,206)	(4,949)
Electricity Revenues [Member] | Crude Oil Price Swap [Member]
Call options on natural gas price			2,728
Electricity Revenues [Member] | Natural Gas Price Swap [Member]
Call options on natural gas price		$ 1,158	$ 2,996