Note 6 - Accumulated Loss of Unconsolidated Company in Excess of Investment (Details)		3 Months Ended								12 Months Ended
	Jun. 04, 2014 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Sep. 30, 2014 USD ($)	Jun. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	Dec. 31, 2015 USD ($) MW	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	May. 23, 2014 USD ($)	May. 16, 2014 USD ($)
Note 6 - Accumulated Loss of Unconsolidated Company in Excess of Investment (Details) [Line Items]
Number of Commercial Lenders in Funding Consortium														6
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax										$ 91,000	$ (902,000)
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest		$ 24,148,000	$ 73,661,000	$ 15,273,000	$ 10,267,000	$ 7,143,000	$ 16,770,000	$ 9,313,000	$ 21,789,000	123,349,000	$ 55,015,000	$ 42,031,000
Intersegment Eliminations [Member]
Note 6 - Accumulated Loss of Unconsolidated Company in Excess of Investment (Details) [Line Items]
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest										$ 6,700,000
London Interbank Offered Rate (LIBOR) [Member]
Note 6 - Accumulated Loss of Unconsolidated Company in Excess of Investment (Details) [Line Items]
Debt Instrument, Basis Spread on Variable Rate										1.00%
Interest Rate Swap [Member]
Note 6 - Accumulated Loss of Unconsolidated Company in Excess of Investment (Details) [Line Items]
Deferred Tax Assets, Derivative Instruments		3,700,000								$ 3,700,000
Sarulla [Member] | Lenders Consortium [Member]
Note 6 - Accumulated Loss of Unconsolidated Company in Excess of Investment (Details) [Line Items]
Senior Notes														$ 1,170,000,000
Sarulla [Member] | Interest Rate Swap [Member]
Note 6 - Accumulated Loss of Unconsolidated Company in Excess of Investment (Details) [Line Items]
Derivative Instruments, Loss Recognized in Other Comprehensive Income (Loss), Effective Portion										20,600,000
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax										2,600,000
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax		10,800,000								10,800,000
Sarulla [Member] | Interest Rate Swap [Member] | Sarulla [Member]
Note 6 - Accumulated Loss of Unconsolidated Company in Excess of Investment (Details) [Line Items]
Deferred Tax Assets, Derivative Instruments		$ 28,600,000								$ 28,600,000
Sarulla [Member]
Note 6 - Accumulated Loss of Unconsolidated Company in Excess of Investment (Details) [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share		12.75%								12.75%
Expected Power Generating Capacity (in Megawatts) | MW										330
Contract Effective Date										Apr. 04, 2013
Power Plant Usage Agreement Term										30 years
Number Of Phases Of Construction										3
Power Utilization (in Megawatts) | MW										110
Period To Start Remaining Phases Of Construction After Commencement Of First Phase										18 months
Supply Commitment, Remaining Minimum Amount Committed		$ 255,600,000								$ 255,600,000
Payments to Acquire Projects										0
Sarulla [Member] | Lenders Consortium [Member] | Subject to Fixed Interest Rate [Member]
Note 6 - Accumulated Loss of Unconsolidated Company in Excess of Investment (Details) [Line Items]
Senior Notes													$ 100,000,000
Sarulla [Member] | Lenders Consortium [Member] | Subject to LIBOR based Interest Rate [Member]
Note 6 - Accumulated Loss of Unconsolidated Company in Excess of Investment (Details) [Line Items]
Senior Notes		1,070,000,000								1,070,000,000
Sarulla [Member] | Interest Rate Swap [Member] | Lenders Consortium [Member]
Note 6 - Accumulated Loss of Unconsolidated Company in Excess of Investment (Details) [Line Items]
Proceeds from Issuance of Senior Long-term Debt	$ 50,000,000
Sarulla [Member] | Interest Rate Swap [Member] | Lenders Consortium [Member] | Subject to Fixed LIBOR Interest Rate [Member]
Note 6 - Accumulated Loss of Unconsolidated Company in Excess of Investment (Details) [Line Items]
Senior Notes		$ 960,000,000								$ 960,000,000
Sarulla [Member] | Interest Rate Swap [Member] | London Interbank Offered Rate (LIBOR) [Member] | Lenders Consortium [Member]
Note 6 - Accumulated Loss of Unconsolidated Company in Excess of Investment (Details) [Line Items]
Debt Instrument, Basis Spread on Variable Rate	3.4565%