ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (Details) - USD ($) $ in Thousands |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2020 |
Jun. 30, 2019 |
Jun. 30, 2020 |
Jun. 30, 2019 |
|
| Accumulated Other Comprehensive Income (Loss) [Line Items] | ||||
| Amortization of net loss | $ 10,623 | $ 8,821 | $ 21,246 | $ 17,642 |
| Amortization of unrecognized prior service cost | (29) | (168) | (58) | (336) |
| Reclassification adjustment, before tax and regulatory adjustments | 10,594 | 8,653 | 21,188 | 17,306 |
| Stranded Deferred Tax Remeasurement Benefit | 0 | 0 | 0 | (1,218) |
| Regulatory adjustments | (10,296) | (8,440) | (20,592) | (15,662) |
| Reclassification adjustment, before tax | 298 | 213 | 596 | 426 |
| Reclassification adjustment, Tax | (75) | (53) | (149) | (106) |
| Reclassification adjustment, net of tax | $ 223 | $ 160 | $ 447 | $ 320 |