Fair Value of Financial Assets and Liabilities, Financial Impact of Qualifying Cash Flow Hedges (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 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	$ (418,000)	$ (495,000)	$ (437,000)	$ (514,000)
After-tax net realized losses on derivative transactions reclassified into earnings	18,000	19,000	37,000	38,000
Accumulated other comprehensive loss related to cash flow hedges at end of period	(400,000)	(476,000)	(400,000)	(476,000)
Pre-tax (gains) losses reclassified into income during the period from regulatory assets and (liabilities)				2,900,000
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		$ 200,000	$ 400,000