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Business Description and Significant Accounting Policies Accounts Receivable (Details) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2012
Dec. 31, 2011
Accounts Receivable [Line Items]    
Allowance for Doubtful Accounts $ (768) $ (1,661)
Accounts receivable, net 163,698 156,774
Electric Utilities [Member]
   
Accounts Receivable [Line Items]    
Allowance for Doubtful Accounts (527) (545)
Accounts receivable, net 77,798 63,379
Gas Utilities [Member]
   
Accounts Receivable [Line Items]    
Allowance for Doubtful Accounts (222) (1,011)
Accounts receivable, net 71,235 77,334
Power Generation [Member]
   
Accounts Receivable [Line Items]    
Allowance for Doubtful Accounts 0 0
Accounts receivable, net 16 282
Coal Mining [Member]
   
Accounts Receivable [Line Items]    
Allowance for Doubtful Accounts 0 0
Accounts receivable, net 2,247 4,056
Oil and Gas [Member]
   
Accounts Receivable [Line Items]    
Allowance for Doubtful Accounts (19) (105)
Accounts receivable, net 11,603 11,177
Corporate [Member]
   
Accounts Receivable [Line Items]    
Allowance for Doubtful Accounts 0 0
Accounts receivable, net 799 546
Billed Revenues [Member]
   
Accounts Receivable [Line Items]    
Accounts Receivable, Trade 100,661 98,292
Billed Revenues [Member] | Electric Utilities [Member]
   
Accounts Receivable [Line Items]    
Accounts Receivable, Trade 54,482 42,773
Billed Revenues [Member] | Gas Utilities [Member]
   
Accounts Receivable [Line Items]    
Accounts Receivable, Trade 31,495 39,353
Billed Revenues [Member] | Power Generation [Member]
   
Accounts Receivable [Line Items]    
Accounts Receivable, Trade 16 282
Billed Revenues [Member] | Coal Mining [Member]
   
Accounts Receivable [Line Items]    
Accounts Receivable, Trade 2,247 4,056
Billed Revenues [Member] | Oil and Gas [Member]
   
Accounts Receivable [Line Items]    
Accounts Receivable, Trade 11,622 11,282
Billed Revenues [Member] | Corporate [Member]
   
Accounts Receivable [Line Items]    
Accounts Receivable, Trade 799 546
Unbilled Revenues [Member]
   
Accounts Receivable [Line Items]    
Accounts Receivable, Trade 63,805 60,143
Unbilled Revenues [Member] | Electric Utilities [Member]
   
Accounts Receivable [Line Items]    
Accounts Receivable, Trade 23,843 21,151
Unbilled Revenues [Member] | Gas Utilities [Member]
   
Accounts Receivable [Line Items]    
Accounts Receivable, Trade 39,962 38,992
Unbilled Revenues [Member] | Power Generation [Member]
   
Accounts Receivable [Line Items]    
Accounts Receivable, Trade 0 0
Unbilled Revenues [Member] | Coal Mining [Member]
   
Accounts Receivable [Line Items]    
Accounts Receivable, Trade 0 0
Unbilled Revenues [Member] | Oil and Gas [Member]
   
Accounts Receivable [Line Items]    
Accounts Receivable, Trade 0 0
Unbilled Revenues [Member] | Corporate [Member]
   
Accounts Receivable [Line Items]    
Accounts Receivable, Trade $ 0 $ 0