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Summary of Significant Accounting Policies (Details Textual) (USD $)
12 Months Ended
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Schedule of Equity Method Investments [Line Items]      
Ownership interest in Equity Method Investment 50.00%    
Summary of Significant Accounting Policies (Textual) [Abstract]      
Maturity period of short-term investments P13W    
Impairments of goodwill $ 0 $ 0 $ 0
Insurance coverage of general liability and auto liability risks 100,000,000    
Insurance policy covering pollution liability 30,000,000    
Tax benefit recognized Greater than 50%    
Asset retirement obligations 75,000    
Assets held for sale $ 0 $ 0  
Minimum [Member]
     
Schedule of Equity Method Investments [Line Items]      
Ownership interest in Equity Method Investment 20.00%    
Maximum [Member]
     
Schedule of Equity Method Investments [Line Items]      
Ownership interest in Equity Method Investment 50.00%