Annual report pursuant to Section 13 and 15(d)

Derivative Financial Instruments (Narrative) (Details)

v2.4.0.6
Derivative Financial Instruments (Narrative) (Details) (USD $)
 12 Months Ended
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Accrued Liabilities [Member]
      
Derivatives, Fair Value [Line Items]      
Fair value of commodity derivative contracts $ 7,200,000 $ 9,500,000  
Prepaid And Other Assets [Member]
      
Derivatives, Fair Value [Line Items]      
Fair value of commodity derivative contracts 2,300,000    
Other Assets [Member]
      
Derivatives, Fair Value [Line Items]      
Fair value of commodity derivative contracts 1,800,000    
Other Long-Term Liabilities [Member]
      
Derivatives, Fair Value [Line Items]      
Fair value of commodity derivative contracts   5,400,000  
Interest Rate Swap Contracts [Member]
      
Derivatives, Fair Value [Line Items]      
Realized gain (loss) on interest derivatives   (4,700,000) (6,500,000)
Unrealized gain (loss) on commodity derivatives   4,400,000 4,700,000
Derivative fixed interest rate   5.21%  
Derivative contract expiration date   Aug. 01, 2010  
Commodity Contract [Member]
      
Derivatives, Fair Value [Line Items]      
Realized gain (loss) on commodity derivatives (9,900,000) 5,500,000 (200,000)
Unrealized gain (loss) on commodity derivatives $ 11,800,000 $ (9,500,000) $ (5,400,000)