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Pension Plans and Other Postretirement Benefit Plans (Tables) | 12 Months Ended
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Dec. 31, 2023
Change in Benefit Obligation and Plan Assets | The following table sets forth the pension and other postretirement benefit plan disclosures as of December 31, 2023 and 2022 and the components of net periodic benefit costs for the years ended December 31, 2023, 2022 and 2021 (dollars in thousands):
|  | Pension Benefits |  |  | Other Post- retirement Benefits |
|  | 2023 |  |  | 2022 |  |  | 2023 |  |  | 2022 |
Change in benefit obligation: |
Benefit obligation as of beginning of year |  | $ | 557,709 |  |  | $ | 799,042 |  |  | $ | 115,635 |  |  | $ | 167,598 |
Service cost |  |  | 14,350 |  |  |  | 23,877 |  |  |  | 2,394 |  |  |  | 4,369 |
Interest cost |  |  | 33,245 |  |  |  | 26,536 |  |  |  | 6,766 |  |  |  | 5,503 |
Actuarial (gain)/loss |  |  | 21,373 |  |  |  | (204,775 | ) |  |  | 4,799 |  |  |  | (54,120 | )
Plan change |  |  | — |  |  |  | 3,302 |  |  |  | — |  |  |  | — |
Settlement |  |  | — |  |  |  | (60,206 | ) |  |  | — |  |  |  | — |
Benefits paid |  |  | (41,432 | ) |  |  | (30,067 | ) |  |  | (7,210 | ) |  |  | (7,715 | )
Benefit obligation as of end of year |  | $ | 585,245 |  |  | $ | 557,709 |  |  | $ | 122,384 |  |  | $ | 115,635 |
Change in plan assets: |
Fair value of plan assets as of beginning of year |  | $ | 540,703 |  |  | $ | 750,963 |  |  | $ | 49,472 |  |  | $ | 59,544 |
Actual return on plan assets |  |  | 78,838 |  |  |  | (163,866 | ) |  |  | 8,654 |  |  |  | (10,072 | )
Employer contributions |  |  | 10,000 |  |  |  | 42,000 |  |  |  | — |  |  |  | — |
Settlement |  |  | — |  |  |  | (60,206 | ) |  |  | — |  |  |  | — |
Benefits paid |  |  | (39,558 | ) |  |  | (28,188 | ) |  |  | — |  |  |  | — |
Fair value of plan assets as of end of year |  | $ | 589,983 |  |  | $ | 540,703 |  |  | $ | 58,126 |  |  | $ | 49,472 |
Funded status |  | $ | 4,738 |  |  | $ | (17,006 | ) |  | $ | (64,258 | ) |  | $ | (66,163 | )
Amounts recognized in the Consolidated Balance Sheets: |
Other non-current assets |  | $ | 32,997 |  |  | $ | 13,382 |  |  | $ | — |  |  | $ | — |
Other current liabilities |  |  | (2,212 | ) |  |  | (1,934 | ) |  |  | (652 | ) |  |  | (706 | )
Non-current liabilities |  |  | (26,047 | ) |  |  | (28,454 | ) |  |  | (63,606 | ) |  |  | (65,457 | )
Net amount recognized |  | $ | 4,738 |  |  | $ | (17,006 | ) |  | $ | (64,258 | ) |  | $ | (66,163 | )
Accumulated pension benefit obligation |  | $ | 514,295 |  |  | $ | 495,654 |  |  |  |  |  |  |
Accumulated postretirement benefit obligation: |  |  |  |  |  |  |  |  |  |  |  |
For retirees |  |  |  |  |  |  |  | $ | 68,087 |  |  | $ | 61,984 |
For fully eligible employees |  |  |  |  |  |  |  | $ | 16,054 |  |  | $ | 19,731 |
For other participants |  |  |  |  |  |  |  | $ | 38,243 |  |  | $ | 33,920 |
Included in accumulated other comprehensive loss (income) (net of tax): |
Unrecognized prior service cost (credit) |  | $ | 3,717 |  |  | $ | 4,105 |  |  | $ | (1,081 | ) |  | $ | (1,911 | )
Unrecognized net actuarial loss |  |  | 69,002 |  |  |  | 83,794 |  |  |  | 13,103 |  |  |  | 13,643 |
Total |  |  | 72,719 |  |  |  | 87,899 |  |  |  | 12,022 |  |  |  | 11,732 |
Less regulatory asset |  |  | (71,983 | ) |  |  | (85,198 | ) |  |  | (12,401 | ) |  |  | (12,375 | )
Accumulated other comprehensive loss for unfunded benefit obligation for pensions and other postretirement benefit plans |  | $ | 736 |  |  | $ | 2,701 |  |  | $ | (379 | ) |  | $ | (643 | )
|  | Pension Benefits |  |  | Other Post- retirement Benefits |
|  | 2023 |  |  | 2022 |  |  | 2023 |  |  | 2022 |
Weighted-average assumptions as of December 31: |  |  |  |  |  |  |  |  |  |  |  |
Discount rate for benefit obligation |  |  | 5.86 | % |  |  | 6.10 | % |  |  | 5.83 | % |  |  | 6.10 | %
Discount rate for annual expense |  |  | 6.10 | % |  |  | 3.39 | % |  |  | 6.10 | % |  |  | 3.40 | %
Expected long-term return on plan assets |  |  | 8.30 | % |  |  | 5.80 | % |  |  | 7.20 | % |  |  | 4.70 | %
Rate of compensation increase |  |  | 4.87 | % |  |  | 4.69 | % |  |  |  |  |  |
Medical cost trend pre-age 65 – initial |  |  |  |  |  |  |  |  | 6.50 | % |  |  | 6.25 | %
Medical cost trend pre-age 65 – ultimate |  |  |  |  |  |  |  |  | 5.00 | % |  |  | 5.00 | %
Ultimate medical cost trend year pre-age 65 |  |  |  |  |  |  |  | 2030 |  |  | 2028 |
Medical cost trend post-age 65 – initial |  |  |  |  |  |  |  |  | 6.50 | % |  |  | 6.25 | %
Medical cost trend post-age 65 – ultimate |  |  |  |  |  |  |  |  | 5.00 | % |  |  | 5.00 | %
Ultimate medical cost trend year post-age 65 |  |  |  |  |  |  |  | 2030 |  |  | 2028 |
Components of Net Periodic Benefit Cost |
|  | Pension Benefits |  |  | Other Post-retirement Benefits |
|  | 2023 |  |  | 2022 |  |  | 2021 |  |  | 2023 |  |  | 2022 |  |  | 2021 |
Components of net periodic benefit cost: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Service cost (1) |  | $ | 14,350 |  |  | $ | 23,877 |  |  | $ | 25,306 |  |  | $ | 2,394 |  |  | $ | 4,369 |  |  | $ | 4,114 |
Interest cost |  |  | 33,245 |  |  |  | 26,536 |  |  |  | 26,160 |  |  |  | 6,766 |  |  |  | 5,503 |  |  |  | 5,139 |
Expected return on plan assets |  |  | (43,656 | ) |  |  | (43,872 | ) |  |  | (39,088 | ) |  |  | (3,562 | ) |  |  | (2,799 | ) |  |  | (2,400 | )
Amortization of prior service cost (credit) |  |  | 491 |  |  |  | 257 |  |  |  | 257 |  |  |  | (1,050 | ) |  |  | (1,050 | ) |  |  | (921 | )
Net loss recognition |  |  | 4,915 |  |  |  | 4,180 |  |  |  | 6,645 |  |  |  | 319 |  |  |  | 3,344 |  |  |  | 3,865 |
Settlement loss (2) |  |  | — |  |  |  | 11,828 |  |  |  | — |  |  |  | — |  |  |  | — |  |  |  | — |
Net periodic benefit cost |  | $ | 9,345 |  |  | $ | 22,806 |  |  | $ | 19,280 |  |  | $ | 4,867 |  |  | $ | 9,367 |  |  | $ | 9,797 |
(1) Total service costs in the table above are recorded to the same accounts as labor expense. Labor and benefits expense is recorded to various projects based on whether the work is a capital project or an operating expense. Approximately 40 percent of all labor and benefits is capitalized to utility property and 60 percent is expensed to utility other operating expenses. (2) The settlement loss was deferred as a regulatory asset and is being amortized over 12 years in accordance with regulatory accounting orders.
Schedule of Allocation of Plan Assets | The target investment allocation percentages by asset classes are indicated in the table below:
|  | 2023 |  |  | 2022 |
Equity securities |  |  | 55 | % |  |  | 55 | %
Debt securities |  |  | 40 | % |  |  | 40 | %
Real estate |  |  | 5 | % |  |  | 5 | %
Employer Matching Contributions | Employer matching contributions were as follows for the years ended December 31 (dollars in thousands):
|  | 2023 |  |  | 2022 |  |  | 2021 |
Employer 401(k) matching contributions |  | $ | 15,022 |  |  | $ | 13,258 |  |  | $ | 11,671 |
Deferred Compensation Assets and Liabilities | There were deferred compensation assets included in other property and investments-net and corresponding deferred compensation liabilities included in other non-current liabilities and deferred credits on the Consolidated Balance Sheets of the following amounts as of December 31 (dollars in thousands):
|  | 2023 |  |  | 2022 |
Deferred compensation assets and liabilities |  | $ | 7,794 |  |  | $ | 7,541 |
Pension Plan And SERP [Member] |
Schedule of Expected Benefit Payments | The Company expects benefit payments under the pension plan and the SERP will total (dollars in thousands):
|  | 2024 |  |  | 2025 |  |  | 2026 |  |  | 2027 |  |  | 2028 |  |  | Total 2029- 2033 |
Expected benefit payments |  | $ | 41,562 |  |  | $ | 42,123 |  |  | $ | 42,941 |  |  | $ | 43,517 |  |  | $ | 44,700 |  |  | $ | 232,345 |
Schedule of Allocation of Plan Assets | The following table discloses by level within the fair value hierarchy (see Note 18 for a description of the fair value hierarchy) of the pension plan’s assets measured and reported as of December 31, 2023 at fair value (dollars in thousands):
|  | Level 1 |  |  | Level 2 |  |  | Level 3 |  |  | Total |
Cash equivalents |  | $ | — |  |  | $ | 6,984 |  |  | $ | — |  |  | $ | 6,984 |
Fixed income securities: |  |  |  |  |  |  |  |  |  |  |  |
U.S. government issues |  |  | — |  |  |  | 19,293 |  |  |  | — |  |  |  | 19,293 |
Corporate issues |  |  | — |  |  |  | 175,460 |  |  |  | — |  |  |  | 175,460 |
International issues |  |  | — |  |  |  | 27,052 |  |  |  | — |  |  |  | 27,052 |
Municipal issues |  |  | — |  |  |  | 13,772 |  |  |  | — |  |  |  | 13,772 |
Mutual funds: |  |  |  |  |  |  |  |  |  |  |  |
U.S. equity securities |  |  | 169,993 |  |  |  | — |  |  |  | — |  |  |  | 169,993 |
International equity securities |  |  | 74,749 |  |  |  | — |  |  |  | — |  |  |  | 74,749 |
Plan assets measured at NAV (not subject to hierarchy disclosure) |  |  |  |  |  |  |  |  |  |  |  |
Common/collective trusts: real estate |  |  | — |  |  |  | — |  |  |  | — |  |  |  | 25,284 |
Partnership/closely held investments: |  |  |  |  |  |  |  |  |  |  |  |
International equity securities |  |  | — |  |  |  | — |  |  |  | — |  |  |  | 70,652 |
Real estate |  |  | — |  |  |  | — |  |  |  | — |  |  |  | 6,744 |
Total |  | $ | 244,742 |  |  | $ | 242,561 |  |  | $ | — |  |  | $ | 589,983 |
The following table discloses by level within the fair value hierarchy (see Note 18 for a description of the fair value hierarchy) of the pension plan’s assets measured and reported as of December 31, 2022 at fair value (dollars in thousands):
|  | Level 1 |  |  | Level 2 |  |  | Level 3 |  |  | Total |
Cash equivalents |  | $ | — |  |  | $ | 5,110 |  |  | $ | — |  |  | $ | 5,110 |
Fixed income securities: |  |  |  |  |  |  |  |  |  |  |  |
U.S. government issues |  |  | — |  |  |  | 16,732 |  |  |  | — |  |  |  | 16,732 |
Corporate issues |  |  | — |  |  |  | 161,180 |  |  |  | — |  |  |  | 161,180 |
International issues |  |  | — |  |  |  | 23,108 |  |  |  | — |  |  |  | 23,108 |
Municipal issues |  |  | — |  |  |  | 13,427 |  |  |  | — |  |  |  | 13,427 |
Mutual funds: |  |  |  |  |  |  |  |  |  |  |  |
U.S. equity securities |  |  | 154,442 |  |  |  | — |  |  |  | — |  |  |  | 154,442 |
International equity securities |  |  | 58,933 |  |  |  | — |  |  |  | — |  |  |  | 58,933 |
Plan assets measured at NAV (not subject to hierarchy disclosure) |  |  |  |  |  |  |  |  |  |  |  |
Common/collective trusts: real estate |  |  | — |  |  |  | — |  |  |  | — |  |  |  | 30,406 |
Partnership/closely held investments: |  |  |  |  |  |  |  |  |  |  |  |
International equity securities |  |  | — |  |  |  | — |  |  |  | — |  |  |  | 69,792 |
Real estate |  |  | — |  |  |  | — |  |  |  | — |  |  |  | 7,573 |
Total |  | $ | 213,375 |  |  | $ | 219,557 |  |  | $ | — |  |  | $ | 540,703 |
Other Postretirement Benefits [Member] |
Schedule of Expected Benefit Payments | The Company expects benefit payments under other postretirement benefit plans will total (dollars in thousands):
|  | 2024 |  |  | 2025 |  |  | 2026 |  |  | 2027 |  |  | 2028 |  |  | Total 2029- 2033 |
Expected benefit payments |  | $ | 7,084 |  |  | $ | 7,266 |  |  | $ | 7,436 |  |  | $ | 7,608 |  |  | $ | 7,822 |  |  | $ | 40,805 |

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