Equity Method Investments (Details) (USD $)	1 Months Ended	12 Months Ended			1 Months Ended
	Apr. 30, 2012 mi	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Feb. 28, 2014 mi
Schedule of Equity Method Investments [Line Items]
Net book value		$ 68,029,000	$ 26,892,000
Constitution Pipeline
Schedule of Equity Method Investments [Line Items]
Length of pipeline to be constructed (in miles)	124
Contribution cap	250,000,000
Expected contribution in future years		139,700,000
Number of year's investment expected for contribution		2 years
Contributions		34,200,000	18,900,000	6,900,000
Central Penn Line
Schedule of Equity Method Investments [Line Items]
Length of pipeline to be constructed (in miles)					177
Expected contribution in future years		135,300,000
Number of years investment is expected to occur, new pipeline		3 years
Central Penn Line | Transcontinental Gas Pipe Line Company LLC
Schedule of Equity Method Investments [Line Items]
Entity's equity interest in construction agreement (as a percent)					61.00%
Constitution Pipeline Company, LLC
Schedule of Equity Method Investments [Line Items]
Entity's equity interest in construction agreement (as a percent)	25.00%
Net book value		64,300,000	26,900,000
Meade Pipeline Co LLC
Schedule of Equity Method Investments [Line Items]
Contributions		3,900,000
Net book value		$ 3,800,000
Ownership interest (as a percent)					20.00%
Meade Pipeline Co LLC | Central Penn Line
Schedule of Equity Method Investments [Line Items]
Entity's equity interest in construction agreement (as a percent)					39.00%