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Equity Method Investment (Details) (USD $)
 1 Months Ended 12 Months Ended 1 Months Ended
Dec. 31, 2012
Apr. 30, 2012
Amended and Restated Limited Liability Company Agreement
Dec. 31, 2012
Amended and Restated Limited Liability Company Agreement
Feb. 29, 2012
Precedent Agreement with constitution Pipeline Company, LLC
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Constitution Pipeline Company, LLC        
Length of pipeline to be constructed (in miles)       120
Capacity owned by entity on newly constructed pipeline (in Mcf per day)       500,000
Entity's equity interest in construction agreement (as a percent)   25.00%    
Amount entity agreed to invest   $ 187,000,000    
Contribution cap   250,000,000    
Number of years investment is expected to occur   3 years    
Contributions     6,900,000  
Net book value $ 6,915,000   $ 6,900,000