EMPLOYEE BENEFIT PLANS (Details) - USD ($)
$ in Thousands |
3 Months Ended |
6 Months Ended |
|
Jun. 30, 2020 |
Jun. 30, 2019 |
Jun. 30, 2020 |
Jun. 30, 2019 |
Dec. 31, 2019 |
| Employee Benefit Plans [Line Items] |
|
|
|
|
|
| Document Period End Date |
|
|
Jun. 30, 2020
|
|
|
| Capitalized non-service cost components as a regulatory asset |
$ 5,900
|
|
$ 5,900
|
|
$ 4,700
|
| Components of net periodic benefit cost: |
|
|
|
|
|
| Amortization of unrecognized prior service cost |
29
|
$ 168
|
58
|
$ 336
|
|
| Amortization of net loss |
(10,623)
|
(8,821)
|
(21,246)
|
(17,642)
|
|
| ONE Gas Pension Plans [Member] |
|
|
|
|
|
| Components of net periodic benefit cost: |
|
|
|
|
|
| Service cost |
3,217
|
3,008
|
6,434
|
6,016
|
|
| Interest cost |
8,545
|
10,168
|
17,090
|
20,336
|
|
| Expected return on assets |
(15,280)
|
(15,485)
|
(30,560)
|
(30,970)
|
|
| Amortization of net loss |
10,580
|
8,260
|
21,160
|
16,520
|
|
| Net periodic benefit cost |
7,062
|
5,951
|
14,124
|
11,902
|
|
| ONE Gas Postretirement Benefit Plans [Member] |
|
|
|
|
|
| Components of net periodic benefit cost: |
|
|
|
|
|
| Service cost |
423
|
434
|
846
|
868
|
|
| Interest cost |
1,889
|
2,329
|
3,778
|
4,658
|
|
| Expected return on assets |
(3,867)
|
(3,147)
|
(7,734)
|
(6,294)
|
|
| Amortization of unrecognized prior service cost |
(29)
|
(168)
|
(58)
|
(336)
|
|
| Amortization of net loss |
43
|
561
|
86
|
1,122
|
|
| Net periodic benefit cost |
$ (1,541)
|
$ 9
|
$ (3,082)
|
$ 18
|
|