REGULATORY ASSETS AND LIABILITIES (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Regulatory Assets [Line Items]
Total regulatory assets	$ 309,290	$ 296,081
Environmental Restoration Costs: Expended - Net [Member]
Regulatory Assets [Line Items]
Total regulatory assets	26,590	29,945
Environmental Restoration Costs: Liability for Future Expenditures [Member]
Regulatory Assets [Line Items]
Total regulatory assets	119,604	119,492
Deferred Asset Retirement Obligation Costs [Member]
Regulatory Assets [Line Items]
Total regulatory assets	31,347	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	34,008	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	5,528	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	4,735	3,735
Energy Efficiency Tracker [Member]
Regulatory Assets [Line Items]
Total regulatory assets	7,470	10,420
Pipeline Supplier Service Charges [Member]
Regulatory Assets [Line Items]
Total regulatory assets	6,690	7,106
Pipeline Integrity Cost [Member]
Regulatory Assets [Line Items]
Total regulatory assets	2,962	2,902
AFUDC - Equity Related Deferrals [Member]
Regulatory Assets [Line Items]
Total regulatory assets	8,631	7,810
Other Regulatory Assets [Member]
Regulatory Assets [Line Items]
Total regulatory assets	$ 2,441	$ 2,356