v3.25.2
EMPLOYEE BENEFIT PLANS (Details) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2025
Jun. 30, 2024
Jun. 30, 2025
Jun. 30, 2024
Dec. 31, 2024
Components of net periodic benefit cost:          
Defined benefit plan, amortization of unrecognized prior service (credit) cost $ 93 $ 93 $ (186) $ (186)  
Defined benefit plan, amortization of net gain (loss) 1,834 1,442 3,668 2,884  
Other Deferred Compensation Arrangements, Liability, Current and Noncurrent 20,300   20,300   $ 18,900
Cash Surrender Value of Life Insurance 43,700   43,700   41,500
Deferred Compensation Arrangement with Individual, Compensation Expense     1,100 1,400  
Regulatory Deferral of net periodic benefit costs     (500) 2,400  
Capitalized non-service cost components (6,700)   (6,700)   $ (6,700)
ONE Gas Pension Plans [Member]          
Components of net periodic benefit cost:          
Service cost 1,337 1,551 2,674 3,102  
Interest cost 10,042 10,281 20,084 20,562  
Expected return on assets (11,910) (14,757) (23,820) (29,514)  
Defined benefit plan, amortization of unrecognized prior service (credit) cost 93 93 186 186  
Defined benefit plan, amortization of net gain (loss) 1,865 1,446 3,730 2,892  
Net periodic benefit cost (credit) 1,427 (1,386) 2,854 (2,772)  
ONE Gas Postretirement Benefit Plans [Member]          
Components of net periodic benefit cost:          
Service cost 123 152 246 304  
Interest cost 2,069 2,045 4,138 4,090  
Expected return on assets (2,212) (2,284) (4,424) (4,568)  
Defined benefit plan, amortization of unrecognized prior service (credit) cost 0 0 0 0  
Defined benefit plan, amortization of net gain (loss) (31) (4) (62) (8)  
Net periodic benefit cost (credit) $ (51) $ (91) $ (102) $ (182)