Fair Value of Financial Assets and Liabilities, Financial Impact of Qualifying Cash Flow Hedges (Details) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 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	$ (437,000)	$ (514,000)
After-tax net realized losses on derivative transactions reclassified into earnings	19,000	19,000
Accumulated other comprehensive loss related to cash flow hedges at end of period	(418,000)	(495,000)
Pre-tax fair value gains (losses) recognized during the period in regulatory (assets) and liabilities		(400,000)
Pre-tax (gains) losses reclassified into income during the period from regulatory assets and (liabilities)		$ 2,900,000