ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Accumulated Other Comprehensive Income (Loss) [Line Items]
Defined benefit plan, amortization of net (gain) loss	$ (1,834)	$ (1,442)
Defined benefit plan, amortization of unrecognized prior service cost (credit)	93	93
Defined benefit plan, reclassification adjustment, before tax and regulatory adjustments	(1,927)	(1,535)
Defined benefit plan, regulatory adjustments	1,927	1,535
Debt Securities, Available-for-Sale, Realized Gain (Loss)	3	1
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, before Tax	3	1
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	3	1
Reclassification from AOCI, Current Period, Tax	(1)	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	2	1
ONE Gas Pension Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Defined benefit plan, amortization of net (gain) loss	(1,865)	(1,446)
Defined benefit plan, amortization of unrecognized prior service cost (credit)	(93)	(93)
Defined benefit plan, reclassification from AOCI, Current Period, before Tax, Attributable to Parent	$ 0	$ 0