CREDIT FACILITIES (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)
Short-term Debt [Line Items]
Line of Credit Facility Option to Increase Borrowing Capacity	$ 500,000
Line of Credit Facility, Expiration Date	Oct. 01, 2022
Ratio of Indebtedness to Net Capital	0.41
Commercial paper maximum borrowing capacity	$ 700,000
Commercial Paper	185,000	$ 357,215
Short-term Debt	0
Line of Credit Facility, Remaining Borrowing Capacity	$ 514,200
Line of Credit [Member]
Short-term Debt [Line Items]
Debt Instrument, Covenant Description	The ONE Gas Credit Agreement contains certain financial, operational and legal covenants. Among other things, these covenants include maintaining ONE Gas’ total debt-to-capital ratio of no more than 70 percent at the end of any calendar quarter.