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REGULATORY ASSETS AND LIABILITIES (Details) - USD ($) $ in Thousands | 12 Months Ended |
--- | --- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Jan. 01, 2017
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items] |  |  |  |
Regulatory Assets, Current | $ 54,420 | $ 88,180 |  |
Regulatory Assets, Noncurrent | 437,479 | 405,189 |  |
Regulatory Liability, Current | (48,394) | (9,438) |  |
Regulatory Liability, Noncurrent | (520,866) | (519,421) |  |
Net regulatory assets and liabilities, current | 6,026 | 78,742 |  |
Net regulatory assets and liabilities, noncurrent | (83,387) | (114,232) |  |
Net Regulatory Assets | (77,361) | (35,490) |  |
Amortization of Rate Deferral | $ 1,700 | $ 1,000 | $ 3,800 |
Federal income tax rate changes [Member] |  |  |  |
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items] |  |  |  |
Regulatory Asset, Amortization Period | See Note 13 | See Note 13 |  |
Regulatory Liability, Current | $ (30,934) | $ 0 |  |
Regulatory Liability, Noncurrent | (520,866) | (519,421) |  |
Regulatory Liabilities | $ (551,800) | $ (519,421) |  |
Weather normalization [Member] |  |  |  |
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items] |  |  |  |
Regulatory Asset, Amortization Period | 1 year | 1 year |  |
Regulatory Assets, Current |  | $ 17,461 |  |
Regulatory Assets, Noncurrent |  | 0 |  |
Regulatory Assets |  | $ 17,461 |  |
Regulatory Liability, Current | $ (3,792) |  |  |
Regulatory Liability, Noncurrent | 0 |  |  |
Regulatory Liabilities | $ (3,792) |  |  |
Over-recovered purchased-gas costs [Member] |  |  |  |
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items] |  |  |  |
Regulatory Asset, Amortization Period | 1 year | 1 year |  |
Regulatory Liability, Current | $ (13,668) | $ (9,434) |  |
Regulatory Liability, Noncurrent | 0 | 0 |  |
Regulatory Liabilities | (13,668) | $ (9,434) |  |
Ad valorem tax [Member] |  |  |  |
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items] |  |  |  |
Regulatory Asset, Amortization Period |  | 1 year |  |
Regulatory Liability, Current |  | $ (4) |  |
Regulatory Liability, Noncurrent |  | 0 |  |
Regulatory Liabilities |  | (4) |  |
Total regulated liabilities [Member] |  |  |  |
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items] |  |  |  |
Regulatory Liability, Current | (48,394) | (9,438) |  |
Regulatory Liability, Noncurrent | (520,866) | (519,421) |  |
Regulatory Liabilities | $ (569,260) | $ (528,859) |  |
Under-recovered purchased-gas costs [Member] |  |  |  |
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items] |  |  |  |
Regulatory Asset, Amortization Period | 1 year | 1 year |  |
Regulatory Assets, Current | $ 25,083 | $ 41,238 |  |
Regulatory Assets, Noncurrent | 0 | 0 |  |
Regulatory Assets | $ 25,083 | $ 41,238 |  |
Pension and postretirement benefit costs [Member] |  |  |  |
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items] |  |  |  |
Regulatory Asset, Amortization Period | See Note 12 | See Note 12 |  |
Regulatory Assets, Current | $ 23,384 | $ 25,156 |  |
Regulatory Assets, Noncurrent | 421,726 | 387,582 |  |
Regulatory Assets | $ 445,110 | $ 412,738 |  |
Reacquired debt costs [Member] |  |  |  |
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items] |  |  |  |
Regulatory Asset, Amortization Period | 9 years | 10 years |  |
Regulatory Assets, Current | $ 812 | $ 812 |  |
Regulatory Assets, Noncurrent | 6,487 | 7,298 |  |
Regulatory Assets | $ 7,299 | $ 8,110 |  |
MGP Costs [Member] |  |  |  |
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items] |  |  |  |
Regulatory Asset, Amortization Period | 15 years | 15 years |  |
Regulatory Assets, Current | $ 0 | $ 0 |  |
Regulatory Assets, Noncurrent | 7,724 | 6,104 |  | $ 5,900
Regulatory Assets | $ 7,724 | $ 6,104 |  |
Ad valorem tax [Member] |  |  |  |
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items] |  |  |  |
Regulatory Asset, Amortization Period | 1 year |  |  |
Regulatory Assets, Current | $ 1,070 |  |  |
Regulatory Assets, Noncurrent | 0 |  |  |
Regulatory Assets | $ 1,070 |  |  |
Other regulatory assets [Member] |  |  |  |
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items] |  |  |  |
Regulatory Asset, Amortization Period | 1 to 20 years | 1 to 21 years |  |
Regulatory Assets, Current | $ 4,071 | $ 3,513 |  |
Regulatory Assets, Noncurrent | 1,542 | 4,205 |  |
Regulatory Assets | 5,613 | 7,718 |  |
Total regulatory assets, net of amortization [Member] |  |  |  |
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items] |  |  |  |
Regulatory Assets, Current | 54,420 | 88,180 |  |
Regulatory Assets, Noncurrent | 437,479 | 405,189 |  |
Regulatory Assets | $ 491,899 | $ 493,369 |  |

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- Definition [Line Items] for Tabular disclosure of assets and liabilities that result from rate actions of a regulator. Regulatory assets are created when regulatory agencies permit public utilities to defer certain costs included in rate-setting to the balance sheet. Rate actions of a regulator can impose a liability on a regulated enterprise resulting in a regulatory liability. + References No definition available. + Details
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- Definition The periodic expense to reduce the value of the rate deferral asset that is created when utilities under bill customers during periods of rate increases by deferring rate increases. These customers eventually pay higher rates to repay the utility for the rate deferral. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585 + Details
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- Definition Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are expected to be recovered through revenue sources within one year or the normal operating cycle, if longer. Such costs are capitalized if they meet both of the following criteria: a. It is probable that future revenue in an amount at least equal to the capitalized cost will result from inclusion of that cost in allowable costs for rate-making purposes. b. Based on available evidence, the future revenue will be provided to permit recovery of the previously incurred cost rather than to provide for expected levels of similar future costs. If the revenue will be provided through an automatic rate-adjustment clause, this criterion requires that the regulator's intent clearly be to permit recovery of the previously incurred cost. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 340 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382 + Details
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