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Note 6 - Fair Value of Financial Instruments (Details) - Significant Unobservable Inputs (USD $)
In Thousands, unless otherwise specified
 3 Months Ended 12 Months Ended
Sep. 30, 2012
MWh
Dec. 31, 2012
MWh
Fair Value Inputs, Assets, Quantitative Information [Line Items]    
Generation output (MWh) 15,097ora_FairValueInputsGenerationOutput 224,836ora_FairValueInputsGenerationOutput
Average realized price ($/MWh) 60.36ora_FairValueInputsAverageRealizedPrice 92.31ora_FairValueInputsAverageRealizedPrice
Operating costs $ 400ora_FairValueInputsOperatingCosts $ 16,163ora_FairValueInputsOperatingCosts
Minimum [Member]    
Fair Value Inputs, Assets, Quantitative Information [Line Items]    
Generation output (MWh) 11,916ora_FairValueInputsGenerationOutput
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		  
Average realized price ($/MWh) 49.00ora_FairValueInputsAverageRealizedPrice
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		 84.50ora_FairValueInputsAverageRealizedPrice
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
Operating costs 86ora_FairValueInputsOperatingCosts
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		 12,687ora_FairValueInputsOperatingCosts
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
Maximum [Member]    
Fair Value Inputs, Assets, Quantitative Information [Line Items]    
Generation output (MWh) 15,456ora_FairValueInputsGenerationOutput
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		  
Average realized price ($/MWh) 71.50ora_FairValueInputsAverageRealizedPrice
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		 111.25ora_FairValueInputsAverageRealizedPrice
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
Operating costs $ 595ora_FairValueInputsOperatingCosts
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		 $ 20,430ora_FairValueInputsOperatingCosts
/ us-gaap_RangeAxis
= us-gaap_MaximumMember