Note 6 - Fair Value of Financial Instruments (Details) - Amounts of Gain (Loss) Recognized in Condensed Consolidated Statements on Derivative Instruments not Designated as Hedges (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized	$ 775	$ 895	$ 2,716
Electricity Revenues [Member] | Oil Price Put Option [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized		(1,330)	(807)
Electricity Revenues [Member] | Natural Gas Price Put Option [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized			(1,342)
Electricity Revenues [Member] | Crude Oil Price Swap [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized	2,728	(635)	1,598
Electricity Revenues [Member] | Natural Gas Price Swap [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized	2,996	(3,052)	2,804
Foreign Currency Gain (Loss) [Member] | Forward Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized	$ (4,949)	$ 5,912	$ 463