Rate and Regulatory Matters (Details Textual) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012
Settlement Agreement [Line Items]
Percentage Of Capacity Representing Non Opposing Customers	99.50%
Annual Cost Of Service	$ 466.5
General System Firm Transportation Rate Per Unit	0.44
General System Firm Transportation Rate Increase	7.40%
Minimum [Member]
Settlement Agreement [Line Items]
Duration Of Effective Period Of Rate Case Settlement	3 years
Maximum [Member]
Settlement Agreement [Line Items]
Duration Of Effective Period Of Rate Case Settlement	5 years