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Fair Value of Financial Instruments - Additional Information (Detail) (USD $)
3 Months Ended 12 Months Ended 1 Months Ended 12 Months Ended 3 Months Ended 12 Months Ended 1 Months Ended 12 Months Ended 12 Months Ended
Dec. 31, 2012
Sep. 30, 2012
Dec. 31, 2012
Sep. 27, 2012
Entity
Apr. 30, 2012
bbl
Dec. 31, 2010
Jun. 30, 2010
Retained Earnings
FSP FAS 115-2 and FAS 124-2
Jun. 30, 2010
Accumulated Other Comprehensive Income
FSP FAS 115-2 and FAS 124-2
Dec. 31, 2011
Auction Rate Securities
Dec. 31, 2012
Put Options Purchased
Oct. 11, 2012
Put Options Purchased
MMBTU
Sep. 27, 2012
Put Options Purchased
Jul. 31, 2012
Put Options Purchased
MMBTU
May 31, 2012
Put Options Purchased
MMBTU
Dec. 31, 2012
Put Options Purchased
Transaction One
Dec. 31, 2012
Put Options Purchased
Transaction Two
Sep. 30, 2012
North Brawley Geothermal Power Plant
Fair Value, Measurements, Nonrecurring
Dec. 31, 2012
North Brawley Geothermal Power Plant
Fair Value, Measurements, Nonrecurring
Sep. 27, 2012
Minimum
May 31, 2012
Minimum
Apr. 30, 2012
Minimum
Oct. 11, 2012
Minimum
Put Options Purchased
Sep. 27, 2012
Maximum
MW
May 31, 2012
Maximum
Apr. 30, 2012
Maximum
MW
Oct. 11, 2012
Maximum
Put Options Purchased
Dec. 31, 2012
United States of America
Dec. 31, 2011
United States of America
Dec. 31, 2012
United States of America
North Brawley Geothermal Power Plant
MW
Dec. 31, 2012
United States of America
Southern California Edison Company
MW
Dec. 31, 2012
United States of America
OREG 4 power plant
MW
Dec. 31, 2012
United States of America
Minimum
North Brawley Geothermal Power Plant
MW
Dec. 31, 2012
United States of America
Maximum
North Brawley Geothermal Power Plant
MW
Apr. 30, 2012
Nymex Heating Oil Swap Contract
Sep. 27, 2012
Nymex Heating Oil Swap Contract
Put Options Purchased
bbl
Apr. 30, 2012
Ice Brent Swap Contract
Sep. 27, 2012
Ice Brent Swap Contract
Put Options Purchased
bbl
Carrying Amounts and Fair Values of Financial Instruments or Liabilities [Line Items]                                                                          
Auction rate securities par values           $ 4,500,000                                                              
Consideration for the sale of securities                 2,822,000                                                        
Cumulative effect of adopting guidance             693,000 (693,000)                                                          
Cumulative effect of adopting guidance, tax               377,000                                                          
Derivative contract percentage                                                                   85.00%   15.00%  
Contracts effective date                                     Jan. 01, 2013 Jul. 01, 2012 May 01, 2012 Jan. 01, 2013 Dec. 31, 2013 Dec. 31, 2012 Mar. 01, 2013 Dec. 31, 2013                      
Energy rate for the Puna complex as a result of fluctuations in oil prices                                             25   25                        
Volume of Swap contract         241,250           8,900,000   700,000 4,400,000                                         191,250   33,750
Fixed rate payments from bank on each settlement                                                                   130.50   115.50  
Derivative contract, strike price                     4.00   3.19 3.08                                         126.63   106.80
Upfront costs of contract                       2,600,000     1,200,000 100,000                                          
Number of banks with company entered into contract       2                                                                  
Loss on swap contract                   2,300,000                                                      
Expected capacity of power for operations                                                         50                
Capacity of power for operations                                                               20 33        
Capacity of plant                                                           27              
Asset fair value                                                         32,000,000   3,600,000            
Impairment loss 229,113,000 7,264,000 236,377,000                                                   229,100,000   7,300,000            
Percentage of discount rate                                 8.00% 8.00%                                      
Net book value of property, plant and equipment, including Construction-in-process                                                     1,261,520,000 1,625,961,000     65,500,000            
Excess of estimated undiscounted cash flows over carrying value of plant                                                             $ 31,200,000            
Approximate generating capacity of plant                                                             10