ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss	$ (126)	$ (1,182)	$ (704)
Other Comprehensive (Income) Loss, Defined Benefit Plan, Before Reclassification Adjustment from AOCI, Tax	(281)	140
Other Comprehensive (Income) Loss, Defined Benefit Plan, before Reclassification Adjustment, after Tax	961	(477)
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, Tax	0	0
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, after Tax	(1)	(1)
Other comprehensive income (loss)	1,056	(478)	5,823
OCI, Debt Securities, Available-for-Sale, Gain (Loss), before Adjustment, Tax	(24)
OCI, Debt Securities, Available-for-Sale, Gain (Loss), before Adjustment, after Tax	94
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax	(1)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	2
Defined benefit plan, amortization of net (gain) loss	(5,770)	(1,960)	(17,010)
Defined benefit plan, amortization of unrecognized prior service cost	372	525	289
Defined benefit plan, reclassification adjustment, before tax and regulatory adjustments	(6,142)	(2,485)	(17,299)
Defined benefit plan, regulatory adjustments	(6,143)	(2,486)	(17,141)
Debt Securities, Available-for-Sale, Realized Gain (Loss)	(3)	0	0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, before Tax	(3)	0	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	(2)	1	(158)
Reclassification from AOCI, Current Period, Tax	1	0	36
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(1)	1	(122)
ONE Gas Pension Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive (Income) Loss, Defined Benefit Plan, Before Reclassification Adjustment from AOCI, Tax	(281)	140	(1,705)
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, after Tax	(1)	1	159
Defined benefit plan, amortization of net (gain) loss	(5,786)	(2,008)	(16,793)
Defined benefit plan, amortization of unrecognized prior service cost	(372)	(372)	(248)
Defined benefit plan, reclassification from AOCI, Current Period, before Tax, Attributable to Parent	$ 1	$ 1	$ (158)