Fair Value of Financial Assets and Liabilities, Financial Impact of Qualifying Cash Flow Hedges (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Financial Impact of Qualifying Cash Flow Hedges on Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated other comprehensive loss related to cash flow hedges at beginning of period	$ (400,000)	$ (476,000)	$ (437,000)	$ (514,000)
After-tax net realized losses on derivative transactions reclassified into earnings	20,000	20,000	57,000	58,000
Accumulated other comprehensive loss related to cash flow hedges at end of period	(380,000)	(456,000)	(380,000)	(456,000)
Pre-tax (gains) losses reclassified into income during the period from regulatory assets and (liabilities)				2,900,000
Derivative instruments designated as fair value hedges	0	0	0	0
Natural Gas Commodity Contract [Member] | Cash Flow Hedging Other [Member]
Financial Impact of Qualifying Cash Flow Hedges on Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Pre-tax fair value gains (losses) recognized during the period in regulatory (assets) and liabilities	$ (200,000)		$ (400,000)	$ (400,000)