ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (Details) - USD ($)
$ in Thousands |
12 Months Ended |
Dec. 31, 2019 |
Dec. 31, 2018 |
Dec. 31, 2017 |
| Accumulated Other Comprehensive Income (Loss) [Line Items] |
|
|
|
| Accumulated Other Comprehensive Income (Loss), beginning balance |
$ (4,086)
|
$ (5,493)
|
|
| Pension and other postretirement benefit plans obligations [Abstract] |
|
|
|
| Other comprehensive income (loss), before reclassification, net of tax |
(2,074)
|
596
|
|
| Amounts reclassified from accumulated other comprehensive income (loss), net of tax |
639
|
811
|
|
| Other comprehensive income (loss), net of tax |
(1,435)
|
1,407
|
$ (778)
|
| Accumulated Other Comprehensive Income (Loss), ending balance |
(6,739)
|
(4,086)
|
(5,493)
|
| Pension and other postretirement benefit plans obligations [Abstract] |
|
|
|
| Amortization of net loss |
35,283
|
43,800
|
42,591
|
| Amortization of unrecognized prior service cost |
(673)
|
(4,567)
|
(4,597)
|
| Other comprehensive income (loss) reclassification adjustment, before tax and regulatory adjustments |
34,610
|
39,233
|
37,994
|
| Other comprehensive income (loss) reclassification - regulatory adjustments |
(33,758)
|
(38,151)
|
(37,157)
|
| Other comprehensive income (loss) reclassification adjustment, before tax |
852
|
1,082
|
837
|
| Other comprehensive income (loss) reclassification adjustment, Tax |
(213)
|
(271)
|
(322)
|
| Other comprehensive income (loss) reclassification adjustment, net of tax |
639
|
$ 811
|
$ 515
|
| Stranded Deferred Tax Remeasurement Benefit |
$ (1,218)
|
|
|