SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Accounting Policies [Abstract]
TEFA and PUA included in both utility revenue and cost of sales	$ 6,000,000	$ 8,000,000	$ 8,600,000
Decrease in TEFA revenue based tax rate		25.00%
Utility Plant:
Production Plant	296,000	299,000
Storage Plant	20,316,000	18,894,000
Transmission Plant	250,886,000	237,375,000
Distribution Plant	1,297,619,000	1,172,462,000
General Plant	49,586,000	51,621,000
Other Plant	1,855,000	3,665,000
Utility Plant in Service	1,620,558,000	1,484,316,000
Construction Work in Progress	38,232,000	30,958,000
Total Utility Plant	1,658,790,000	1,515,274,000
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO as of January 1,	29,388,000	27,925,000
Accretion	1,870,000	1,396,000
Additions	989,000	460,000
Settlements	(1,603,000)	(872,000)
Revisions in Estimated Cash Flows	8,248,000	479,000
ARO as of December 31,	38,892,000	29,388,000	27,925,000
Composite annual rate for all depreciable utility property	2.40%	2.30%	2.40%
Interest capitalized	$ 6,500,000	$ 1,100,000	$ 400,000