Contingent Liabilities and Commitments (Details Textual) (USD $)	6 Months Ended
	Jun. 30, 2012 issues	Dec. 31, 2011
Rate Matters [Abstract]
Number Of Rate Proceeding Issues Unresolved	1
Environmental Matters [Abstract]
Aggregate, Loss Exposure Not Accrued, Low Estimate	$ 7,000,000
Aggregate, Loss Exposure Not Accrued, High Estimate	9,000,000
Accrual for Environmental Loss Contingencies, Total	3,100,000	3,500,000
Accrued Environmental Loss Contingencies, Current	800,000	800,000
Accrued Environmental Loss Contingencies, Noncurrent	2,300,000	2,700,000
Capital Additions [Member]
Commitments For Construction [Abstract]
Purchase Commitment, Remaining Minimum Amount Committed	312,100,000
Potentially Responsible Party At Various Superfund And State Waste Disposal Sites [Member]
Environmental Matters [Abstract]
Aggregate, Loss Exposure Not Accrued, High Estimate	500,000
Environmental Restoration Costs [Member]
Environmental Matters [Abstract]
Regulatory Assets	0	0
Minimum [Member]
Environmental Matters [Abstract]
Expected Duration Of Environmental Assessment And Remediation Spending	3 years
Estimated Capital Costs For Compliance With Hazardous Air Pollutant Regulations	18,000,000
Pipeline Integrity Regulations [Abstract]
Cost To Complete Required Initial Assessments	18,000,000
Maximum [Member]
Environmental Matters [Abstract]
Expected Duration Of Environmental Assessment And Remediation Spending	5 years
Estimated Capital Costs For Compliance With Hazardous Air Pollutant Regulations	23,000,000
Pipeline Integrity Regulations [Abstract]
Cost To Complete Required Initial Assessments	$ 33,000,000