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SHARE-BASED PAYMENTS (Details) - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Feb. 03, 2014
Jan. 31, 2014
Share-based Payments [Line Items]          
Common Stock, Capital Shares Reserved for Future Issuance 2,800,000        
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant 1,400,000        
Share Price         $ 68.22
Volume-weighted average share price of ONE Gas stock on February 3, 2014       $ 33.50  
Share-based compensation expense, net of tax $ 5,700 $ 7,000 $ 9,700    
Share-based compensation, tax benefit 3,500 4,400 6,100    
Employee Stock Award Program Compensation Expense $ 9,187 $ 7,613 $ 0    
Employee Stock Purchase Plan [Member]          
Share-based Payments [Line Items]          
Description Subject to certain exclusions, all employees who work at least 20 hours per week are eligible to participate in the ESPP.  Employees can choose to have up to 10 percent of their annual base pay withheld to purchase our common stock, subject to terms and limitations of the plan. The purchase price of the stock is 85 percent of the lower of the average market price of our common stock on the grant date or exercise date.        
Employee Stock Award Program [Member]          
Share-based Payments [Line Items]          
Description Under the program, each time the per-share closing price of our common stock on the NYSE closed for the first time at or above each $1.00 increment above its previous historical high closing price, we issued, for no monetary consideration, one share of our common stock to all eligible employees.        
Restricted Stock Units (RSUs) [Member]          
Share-based Payments [Line Items]          
Share-based awards conversion ratio upon separation         2.04%
Award vesting period 3 years        
Forfeiture rate maximum (in hundredths) 3.00%        
Total compensation cost not yet recognized $ 3,200        
Total compensation cost not yet recognized, period for recognition 1 year 9 months 18 days        
Nonvested beginning balance (in units) 325,730        
Nonvested beginning balance (in dollars per unit) $ 23.47        
Granted (in units) 75,880        
Weighted -average grant date fair value (per unit) $ 41.40 $ 33.19 $ 47.36    
Vested (in units) (162,280)        
Vested (in dollars per unit) $ 18.32        
Forfeited (in units) (8,072)        
Forfeited (in dollars per unit) $ 34.42        
Nonvested ending balance (in units) 231,258 325,730      
Nonvested ending balance (in dollars per unit) $ 32.59 $ 23.47      
Fair value of shares granted (thousands of dollars) $ 3,141 $ 3,149 $ 1,323    
Performance Unit Awards [Member]          
Share-based Payments [Line Items]          
Share-based awards conversion ratio upon separation         2.04%
Award vesting period 3 years        
Forfeiture rate maximum (in hundredths) 3.00%        
Total compensation cost not yet recognized $ 4,700        
Total compensation cost not yet recognized, period for recognition 1 year 8 months 12 days        
Nonvested beginning balance (in units) 847,951        
Nonvested beginning balance (in dollars per unit) $ 17.62        
Granted (in units) 100,860        
Weighted -average grant date fair value (per unit) $ 44.48 $ 35.98 $ 52.30    
Vested (in units) (502,474)        
Vested (in dollars per unit) $ 14.33        
Forfeited (in units) (7,087)        
Forfeited (in dollars per unit) $ 30.22        
Nonvested ending balance (in units) 439,250 847,951      
Nonvested ending balance (in dollars per unit) $ 27.35 $ 17.62      
Fair value of shares granted (thousands of dollars) $ 4,486 $ 4,462 $ 2,926    
Expected volatility rate 15.90% 18.40% 22.27%    
Expected dividend yield 2.90% 3.37% 3.04%    
Risk-free interest rate 1.10% 0.67% 0.42%    
Employee Stock Purchase Plan [Member]          
Share-based Payments [Line Items]          
Common Stock, Capital Shares Reserved for Future Issuance 700,000        
Maximum allowable percentage of annual base pay withheld to purchase common stock 10.00%        
Purchase price percentage of the lower of its grant date or exercise date market price (in hundredths) 85.00%        
Percent of employees who participated in the Employee Stock Purchase Plan 40.00% 36.00%      
Shares sold under employee stock purchase plan 51,092 51,418      
Share price of shares sold under Employee Stock Purchase Plan in dollars per share $ 36.15 $ 32.29      
Employee Stock Purchase Plan Compensation Expense $ 1,300 $ 400 $ 2,700    
Employee Stock Award Program [Member]          
Share-based Payments [Line Items]          
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized 125,000        
Shares issued to employees under the Employee Stock Award Program 23,506 35,324      
Employee Stock Award Program Compensation Expense $ 1,100 $ 2,500 $ 4,200