EMPLOYEE BENEFIT PLANS (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Dec. 31, 2024
Components of net periodic benefit cost:
Defined benefit plan, amortization of unrecognized prior service cost (credit)	$ (93)	$ (93)
Defined benefit plan, amortization of net (gain) loss	1,834	1,442
Other Deferred Compensation Arrangements, Liability, Current and Noncurrent	19,000		$ 18,900
Cash Surrender Value of Life Insurance	41,700		41,500
Deferred Compensation Arrangement with Individual, Compensation Expense	(300)	1,100
Regulatory Deferral of net periodic benefit costs	(300)	1,000
Capitalized non-service cost components	(6,700)		$ (6,700)
ONE Gas Pension Plans [Member]
Components of net periodic benefit cost:
Service cost	1,337	1,551
Interest cost	10,042	10,281
Expected return on assets	(11,910)	(14,757)
Defined benefit plan, amortization of unrecognized prior service cost (credit)	93	93
Defined benefit plan, amortization of net (gain) loss	1,865	1,446
Net periodic benefit cost (credit)	1,427	(1,386)
ONE Gas Postretirement Benefit Plans [Member]
Components of net periodic benefit cost:
Service cost	123	152
Interest cost	2,069	2,045
Expected return on assets	(2,212)	(2,284)
Defined benefit plan, amortization of unrecognized prior service cost (credit)	0	0
Defined benefit plan, amortization of net (gain) loss	(31)	(4)
Net periodic benefit cost (credit)	$ (51)	$ (91)