Note 5 - Fair Value of Financial Instruments (Details) - Financial Assets and Liabilities at Fair Value - USD ($) $ in Thousands		Jun. 30, 2015	Dec. 31, 2014
Current assets:
Cost or Amortized Cost		$ 137,665	$ 40,230
Fair Value		164,053	85,076
Derivatives:
Fair Value		161,850	86,323
Forward Contracts [Member]
Derivatives:
Fair Value	[1]	707
Derivatives:
Fair Value	[1]	$ (2,899)	(2,882)
Natural Gas Price Swap [Member]
Derivatives:
Fair Value	[2]		4,129
Derivatives:
Fair Value	[2]	$ (11)
Reported Value Measurement [Member]
Current assets:
Cost or Amortized Cost		164,053	85,076
Derivatives:
Cost or Amortized Cost		161,850	86,323
Reported Value Measurement [Member] | Forward Contracts [Member]
Derivatives:
Cost or Amortized Cost	[1]	707
Derivatives:
Cost or Amortized Cost	[1]	$ (2,899)	(2,882)
Reported Value Measurement [Member] | Natural Gas Price Swap [Member]
Derivatives:
Cost or Amortized Cost	[2]		4,129
Derivatives:
Cost or Amortized Cost	[2]	$ (11)
Fair Value, Inputs, Level 1 [Member]
Current assets:
Fair Value		164,053	85,076
Derivatives:
Fair Value		$ 164,053	$ 85,076
Fair Value, Inputs, Level 1 [Member] | Forward Contracts [Member]
Derivatives:
Fair Value	[1]
Fair Value, Inputs, Level 1 [Member] | Natural Gas Price Swap [Member]
Derivatives:
Fair Value	[2]
Derivatives:
Fair Value	[2]
Fair Value, Inputs, Level 2 [Member]
Derivatives:
Fair Value		$ (2,203)	$ 1,247
Fair Value, Inputs, Level 2 [Member] | Forward Contracts [Member]
Derivatives:
Fair Value	[1]	707
Derivatives:
Fair Value	[1]	$ (2,899)	(2,882)
Fair Value, Inputs, Level 2 [Member] | Natural Gas Price Swap [Member]
Derivatives:
Fair Value	[2]		$ 4,129
Derivatives:
Fair Value	[2]	$ (11)
Fair Value, Inputs, Level 3 [Member] | Forward Contracts [Member]
Derivatives:
Fair Value	[1]
Fair Value, Inputs, Level 3 [Member] | Natural Gas Price Swap [Member]
Derivatives:
Fair Value	[2]
Derivatives:
Fair Value	[2]

[1] These amounts relate to derivatives which represent currency forward contracts valued primarily based on observable inputs, including forward and spot prices for currencies, netted against contracted rates and then multiplied against notional amounts, and are included within "accounts payable and accrued expenses" on June 30, 2015 and December 31, 2014, in the consolidated balance sheet with the corresponding gain or loss being recognized within "foreign currency translation and transaction losses" in the consolidated statement of operations and comprehensive income.

[2] This amount relates to a swap contract on natural gas prices, valued primarily based on observable inputs, including forward and spot prices for related commodity indices, and is included within "prepaid expenses and other" and "accounts payable and accrued expenses" on June 30, 2015 and December 31, 2014, respectively, in the consolidated balance sheets with the corresponding gain or loss being recognized within "electricity revenue" in the consolidated statement of operations and comprehensive income.