ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), beginning balance	$ (7,777)	$ (6,739)
Pension and other postretirement benefit plans obligations [Abstract]
Other comprehensive income (loss), before reclassification, net of tax	78	(1,932)
Amounts reclassified from accumulated other comprehensive income (loss), net of tax	1,172	894
Other comprehensive income (loss), net of tax	1,250	(1,038)	$ (1,435)
Accumulated Other Comprehensive Income (Loss), ending balance	(6,527)	(7,777)	(6,739)
Pension and other postretirement benefit plans obligations [Abstract]
Amortization of net loss	45,896	42,492	35,283
Amortization of unrecognized prior service cost	(279)	(117)	(673)
Other comprehensive income (loss) reclassification adjustment, before tax and regulatory adjustments	45,617	42,375	34,610
Other comprehensive income (loss) reclassification - regulatory adjustments	(44,055)	(41,183)	(33,758)
Other comprehensive income (loss) reclassification adjustment, before tax	1,562	1,192	852
Other comprehensive income (loss) reclassification adjustment, Tax	(390)	(298)	(213)
Other comprehensive income (loss) reclassification adjustment, net of tax	1,172	894	$ 639
Other Comprehensive Income (Loss) before Reclassifications, Tax	11	587
Reclassification from AOCI, Current Period, Tax	$ 390	$ 298