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Other Comprehensive Income and Financial Instruments (Details Textuals) (USD $)
In Millions, unless otherwise specified
6 Months Ended
Jun. 30, 2011
Jun. 30, 2010
Jun. 30, 2011
Fuel hedges [Member]
Dec. 31, 2010
Fuel hedges [Member]
Dec. 08, 2010
Costless collar agreements [Member]
ShortTons
Jun. 30, 2011
Commodity Hedges [Member]
Dec. 31, 2010
Commodity Hedges [Member]
Dec. 08, 2010
Written call option [Member]
ShortTons
Dec. 08, 2010
Purchased put option [Member]
ShortTons
Derivative [Line Items]                  
Aggregated fair values of outstanding hedges, current assets     $ 2.8 $ 1.6   $ 1.8 $ 1.9    
Aggregated fair values of outstanding hedges, current liabilities     $ 0.3 $ 1.9   $ 6.9 $ 6.5    
Notional Amount (in Gallons per Month)               21,000 21,000
Forecasted sales of costless collar agreement         21,000        
Other Comprehensive Income and Financial Instruments (Textuals)                  
Tax rate for other comprehensive income and financial instruments 41.50% 42.00%