REGULATORY ASSETS AND LIABILITIES (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Regulatory Assets [Line Items]
Total regulatory assets	$ 314,725	$ 296,081
Environmental Restoration Costs: Expended - Net [Member]
Regulatory Assets [Line Items]
Total regulatory assets	28,612	29,945
Environmental Restoration Costs: Liability for Future Expenditures [Member]
Regulatory Assets [Line Items]
Total regulatory assets	116,029	119,492
Deferred Asset Retirement Obligation Costs [Member]
Regulatory Assets [Line Items]
Total regulatory assets	31,576	31,142
Deferred Pension and Other Postretirement Benefit Costs [Member]
Regulatory Assets [Line Items]
Total regulatory assets	59,284	59,284
Deferred Gas Costs - Net [Member]
Regulatory Assets [Line Items]
Total regulatory assets	37,371	0
Conservation Incentive Program Receivable [Member]
Regulatory Assets [Line Items]
Total regulatory assets	0	10,526
Societal Benefit Costs Receivable [Member]
Regulatory Assets [Line Items]
Total regulatory assets	3,287	10,408
Premium for Early Retirement of debt [Member]
Regulatory Assets [Line Items]
Total regulatory assets	0	955
Deferred Interest Rate Contracts [Member]
Regulatory Assets [Line Items]
Total regulatory assets	5,494	3,735
Energy Efficiency Tracker [Member]
Regulatory Assets [Line Items]
Total regulatory assets	11,779	10,420
Pipeline Supplier Service Charges [Member]
Regulatory Assets [Line Items]
Total regulatory assets	6,273	7,106
Pipeline Integrity Cost [Member]
Regulatory Assets [Line Items]
Total regulatory assets	3,187	2,902
AFUDC - Equity Related Deferrals [Member]
Regulatory Assets [Line Items]
Total regulatory assets	9,568	7,810
Other Regulatory Assets [Member]
Regulatory Assets [Line Items]
Total regulatory assets	$ 2,265	$ 2,356