v2.4.0.6
Goodwill, transmission system rights, power purchase agreements and development intangible assets and liabilities (Details 2) (USD $)
In Thousands, unless otherwise specified
 12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Components of intangible assets    
Gross balance at the end of the period $ 597,087 $ 675,330
Less: accumulated amortization (76,897) (90,179)
Foreign currency translation adjustment 4,693 (877)
Net balance at the end of the period 524,883 584,274
Gross balances at the end of the period (47,900) (73,394)
Less: accumulated amortization 4,448 1,371
Foreign currency translation adjustment (557) 248
Net balance at the end of the period (44,009) (71,775)
Amortization of intangible assets 65,072 10,216
Transmission system rights
    
Components of intangible assets    
Gross balance at the end of the period   231,669
Foreign currency translation adjustment   (51,387)
Net balance at the end of the period   180,282
Power Purchase Agreements
    
Components of intangible assets    
Gross balance at the end of the period 590,923 639,699
Less: accumulated amortization (76,897) (63,908)
Foreign currency translation adjustment 4,693 (877)
Net balance at the end of the period 518,719 574,914
Gross balances at the end of the period (35,287) (35,288)
Less: accumulated amortization 2,884 398
Foreign currency translation adjustment (557) 127
Net balance at the end of the period (32,960) (34,763)
Amortization of intangible assets 66,168 11,586
Fuel Supply Agreements
    
Components of intangible assets    
Gross balance at the end of the period   33,845
Less: accumulated amortization   (26,271)
Net balance at the end of the period   7,574
Gross balances at the end of the period (12,613) (38,106)
Less: accumulated amortization 1,564 973
Foreign currency translation adjustment   121
Net balance at the end of the period (11,049) (37,012)
Amortization of intangible assets (1,096) (1,370)
Development Costs
    
Components of intangible assets    
Gross balance at the end of the period 6,164 1,786
Net balance at the end of the period $ 6,164 $ 1,786