REGULATORY ASSETS & REGULATORY LIABILITIES (Details) (USD $)	Jun. 30, 2011	Dec. 31, 2010
Regulatory Assets [Line Items]
Total regulatory assets	$ 241,754,000	$ 248,413,000
Regulatory Liabilities [Line Items]
Total regulatory liabilities	56,069,000	69,248,000
Deferred revenues - net [Abstract]
Deferred revenues, regulatory liabilities	20,200,000	4,600,000
Environmental Remediation Costs: Expended - Net [Member]
Regulatory Assets [Line Items]
Total regulatory assets	43,817,000	39,056,000
Environmental Restoration Costs: Liability for Future Expenditures [Member]
Regulatory Assets [Line Items]
Total regulatory assets	82,249,000	87,393,000
Income Taxes - Flowthrough Depreciation [Member]
Regulatory Assets [Line Items]
Total regulatory assets	285,000	774,000
Deferred Asset Retirement Obligation Costs [Member]
Regulatory Assets [Line Items]
Total regulatory assets	24,550,000	24,247,000
Pension Costs [Member]
Regulatory Assets [Line Items]
Total regulatory assets	68,828,000	69,017,000
Conservation Incentive Program Recevable [Member]
Regulatory Assets [Line Items]
Total regulatory assets	2,846,000	12,291,000
Societal Benefit Costs Receivable [Member]
Regulatory Assets [Line Items]
Total regulatory assets	5,987,000	4,216,000
Premium for Early Retirement of debt [Member]
Regulatory Assets [Line Items]
Total regulatory assets	618,000	699,000
Other Regulatory Assets [Member]
Regulatory Assets [Line Items]
Total regulatory assets	12,574,000	10,720,000
Excess Plant Removal Costs [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	47,843,000	48,409,000
Deferred Revenues - Net [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	4,605,000	20,179,000
Other Regulatory Liablities [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	$ 3,621,000	$ 660,000