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, 2016	Mar. 31, 2015
Foreign Currency Gain (Loss) [Member] | Call Option on Natural Gas Price [Member]
Call options on natural gas price	$ 518
Foreign Currency Gain (Loss) [Member] | Call and Put Options on Oil Price [Member]
Call options on natural gas price	(643)
Foreign Currency Gain (Loss) [Member] | Forward Contracts [Member]
Call options on natural gas price	$ 1,814	$ (1,251)
Electricity Revenues [Member] | Natural Gas Price Swap [Member]
Call options on natural gas price		317
Call options on natural gas price	$ 1,689	$ (934)