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Equity Investments And Membership Interests In Joint Ventures (Narrative) (Details) (USD $)
3 Months Ended 6 Months Ended
Jun. 30, 2013
Jun. 30, 2012
Jun. 30, 2013
Jun. 30, 2012
Schedule of Equity Method Investments [Line Items]        
Equity method investment impairment $ 20,482,000 $ 525,583,000 $ 20,482,000 $ 525,583,000
Impairment of equity investment     (15,264,000)  
Future development costs, maximum limit 58,500,000   58,500,000  
Tenaska [Member]
       
Schedule of Equity Method Investments [Line Items]        
equity method investment note receivable write off     5,200,000  
Equity method investment impairment     20,500,000  
Impairment of equity investment     $ (15,264,000)  
Equity Method Investment, Ownership Percentage 35.00%   35.00%