Note 5 - Fair Value of Financial Instruments - Financial Assets and Liabilities at Fair Value (Details) - USD ($) $ in Thousands		Sep. 30, 2017	Dec. 31, 2016
Reported Value Measurement [Member]
Cash equivalents (including restricted cash accounts)		$ 13,497	$ 14,922
		(14,836)	874
Reported Value Measurement [Member] | Put Options on Natural Gas Price [Member]
Derivative Asset, Current	[1]	61
Reported Value Measurement [Member] | Contingent Receivable [Member]
Derivative Asset, Current	[2]	1,125	1,443
Reported Value Measurement [Member] | Contingent Payable [Member]
Derivative Liability, Current	[2]	(25,913)	(11,581)
Reported Value Measurement [Member] | Currency Forward Contracts [Member]
Derivative Asset, Current	[3]	486
Derivative Liability, Current	[3]	(203)	(481)
Reported Value Measurement [Member] | Warrant [Member]
Derivative Liability, Current	[2]	(3,889)	(3,429)
Estimate of Fair Value Measurement [Member]
Cash equivalents (including restricted cash accounts)		13,497	14,922
		(14,836)	874
Estimate of Fair Value Measurement [Member] | Put Options on Natural Gas Price [Member]
Derivative Asset, Current	[1]	61
Estimate of Fair Value Measurement [Member] | Contingent Receivable [Member]
Derivative Asset, Current	[2]	1,125	1,443
Estimate of Fair Value Measurement [Member] | Contingent Payable [Member]
Derivative Liability, Current	[2]	(25,913)	(11,581)
Estimate of Fair Value Measurement [Member] | Currency Forward Contracts [Member]
Derivative Asset, Current	[3]	486
Derivative Liability, Current	[3]	(203)	(481)
Estimate of Fair Value Measurement [Member] | Warrant [Member]
Derivative Liability, Current	[2]	(3,889)	(3,429)
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Cash equivalents (including restricted cash accounts)		13,497	14,922
		13,497	14,922
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member] | Put Options on Natural Gas Price [Member]
Derivative Asset, Current	[1]
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member] | Contingent Receivable [Member]
Derivative Asset, Current	[2]
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member] | Contingent Payable [Member]
Derivative Liability, Current	[2]
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member] | Currency Forward Contracts [Member]
Derivative Asset, Current	[3]
Derivative Liability, Current	[3]
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member] | Warrant [Member]
Derivative Liability, Current	[2]
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Cash equivalents (including restricted cash accounts)
		344	(481)
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member] | Put Options on Natural Gas Price [Member]
Derivative Asset, Current	[1]	61
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member] | Contingent Receivable [Member]
Derivative Asset, Current	[2]
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member] | Contingent Payable [Member]
Derivative Liability, Current	[2]
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member] | Currency Forward Contracts [Member]
Derivative Asset, Current	[3]	486
Derivative Liability, Current	[3]	(203)	(481)
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member] | Warrant [Member]
Derivative Liability, Current	[2]
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Cash equivalents (including restricted cash accounts)
		(28,677)	(13,567)
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member] | Put Options on Natural Gas Price [Member]
Derivative Asset, Current	[1]
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member] | Contingent Receivable [Member]
Derivative Asset, Current	[2]	1,125	1,443
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member] | Contingent Payable [Member]
Derivative Liability, Current	[2]	(25,913)	(11,581)
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member] | Currency Forward Contracts [Member]
Derivative Asset, Current	[3]
Derivative Liability, Current	[3]
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member] | Warrant [Member]
Derivative Liability, Current	[2]	$ (3,889)	$ (3,429)

[1] These amounts relate to natural gas put options, valued primarily based on observable inputs, including spot prices on related commodity indices, and are included within Prepaid expenses and other on September 30, 2017 in the consolidated balance sheets with the corresponding gain or loss being recognized within Derivatives and foreign currency transaction gains (losses) in the consolidated statement of operations and comprehensive income.

[2] These amounts relate to contingent receivables and payables relating to the Viridity acquisition and Guadeloupe power plant purchase transaction, valued primarily based on unobservable inputs and are included within Prepaid expenses and other, Accounts payable and accrued expenses and Other long-term liabilities on September 30, 2017 and within Prepaid expenses and other and Other long-term liabilities on December 31, 2016 in the consolidated balance sheets with the corresponding gain or loss being recognized within Derivatives and foreign currency transaction gains (losses) in the consolidated statement of operations and comprehensive income.

[3] These amounts relate to currency forward contracts valued primarily based on observable inputs, including forward and spot prices for currencies, net of contracted rates and then multiplied by notional amounts, and are included within Prepaid expenses and other and Accounts payable and accrued expenses on September 30, 2017 and December 31, 2016, in the consolidated balance sheet with the corresponding gain or loss being recognized within Derivatives and foreign currency transaction gains (losses) in the consolidated statement of operations and comprehensive income.