Regulatory Assets (Details) (USD $)	12 Months Ended						12 Months Ended
	Dec. 31, 2011 Y	Dec. 31, 2010	Dec. 31, 2011 Deferred taxes	Dec. 31, 2010 Deferred taxes	Dec. 31, 2011 Deferred purchased gas costs	Dec. 31, 2010 Deferred purchased gas costs	Dec. 31, 2010 Other post-retirement benefits other than pensions	Dec. 31, 2009 Other post-retirement benefits other than pensions	Dec. 31, 2011 Other post-retirement benefits other than pensions	Dec. 31, 2011 Other	Dec. 31, 2010 Other
Regulatory Asset
Total regulatory assets	$ 97,227,000	$ 114,659,000	$ 89,224,000	$ 91,004,000	$ 3,132,000	$ 12,466,000	$ 7,327,000		$ 4,168,000	$ 703,000	$ 3,862,000
Amounts classified as other current assets	3,132,000	13,710,000
Total long-term regulatory assets	94,095,000	100,949,000
Future recovery of the unfunded status, other post-retirement benefits (in years)	6
Amortization of post-retirement benefits other than pensions used for rate making purpose							700,000	1,400,000
Regulatory liability, current	$ 2,100,000