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Retirement Benefits (Tables) | 6 Months Ended
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Jun. 30, 2023
Retirement Benefits [Abstract] |
Components of Net Periodic Benefit Cost (Credit) | The components of the net periodic pension benefit cost (credit) were as follows:
| Three Months Ended |  | Six Months Ended
| June 30, 2023 |  | June 30, 2022 |  | June 30, 2023 |  | June 30, 2022
| (Dollars in thousands)
Service cost | $ | 2,234 |  |  | $ | 3,270 |  |  | $ | 4,463 |  |  | $ | 6,570 |
Interest cost | 8,724 |  |  | 5,140 |  |  | 17,433 |  |  | 10,299 |
Expected return on plan assets | (10,187) |  |  | (17,315) |  |  | (20,376) |  |  | (34,629) |
Amortization of prior service cost | 25 |  |  | 53 |  |  | 53 |  |  | 108 |
Amortization of actuarial losses | 2,939 |  |  | 1,157 |  |  | 5,884 |  |  | 2,312 |
Net periodic benefit cost (credit) | $ | 3,735 |  |  | $ | (7,695) |  |  | $ | 7,457 |  |  | $ | (15,340) |
The components of the net periodic other postretirement benefit credit were as follows:
| Three Months Ended |  | Six Months Ended
| June 30, 2023 |  | June 30, 2022 |  | June 30, 2023 |  | June 30, 2022
| (Dollars in thousands)
Service cost | $ | 12 |  |  | $ | 26 |  |  | $ | 26 |  |  | $ | 51 |
Interest cost | 189 |  |  | 109 |  |  | 378 |  |  | 218 |
Amortization of prior service credit | (233) |  |  | (416) |  |  | (468) |  |  | (832) |
Amortization of actuarial gains | (162) |  |  | (77) |  |  | (323) |  |  | (154) |
Net periodic benefit credit | $ | (194) |  |  | $ | (358) |  |  | $ | (387) |  |  | $ | (717) |

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- Definition Tabular disclosure of the components of net benefit costs for pension plans and/or other employee benefit plans including service cost, interest cost, expected return on plan assets, gain (loss), prior service cost or credit, transition asset or obligation, and gain (loss) recognized due to settlements or curtailments. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 715 -SubTopic 20 -Subparagraph (h) -Name Accounting Standards Codification -Paragraph 1 -Section 50 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 + Details
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