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Retirement Benefit Plans (Details) $ in Thousands | 3 Months Ended | 9 Months Ended | 12 Months Ended |
--- | --- | --- | --- | ---
Sep. 30, 2024 USD ($) | Sep. 30, 2023 USD ($) | Sep. 30, 2024 USD ($) | Sep. 30, 2023 USD ($) | Dec. 31, 2022 USD ($) | Dec. 31, 2023
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Interest credit under cash balance plan |  |  | 0.03 |  |  |
Employer matching contribution, percent of match, maximum |  |  | 5.00% |  |  |
Defined benefit plan, service cost and interest cost |  |  |  |  | $ 3,300 |
Defined benefit plan, unamortized net loss |  |  |  |  | $ 7,200 |
Defined benefit plan, benefit obligation from lump sum payment to total benefit obligation ratio (in percent) |  |  |  |  | 8.06% |
Defined benefit plan, net periodic benefit cost, loss due to settlement |  |  |  |  | $ 577 |
Employees' Pension Plan |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Assumptions used calculating benefit obligation, interest rate to annuitize cash balance account |  |  |  |  |  | 5.50%
Defined benefit plan, increase in benefit payable (in percent) | 3.00% |  | 3.00% |  |  |
Defined benefit plan, benefit obligation, increase (decrease) for plan amendment |  |  | $ 351,638 |  |  |
Defined benefit plan, amortization of service cost (in years) |  |  | 9 years 8 months 12 days |  |  |
Net Periodic Benefit Cost |  |  |  |  |  |
Service Cost | $ 423 | $ 398 | $ 1,269 | $ 1,195 |  |
Interest Cost (Benefit) | 562 |  |  |  |  |
Interest Cost |  | 524 | 1,682 | 1,573 |  |
Expected Return on Plan Assets | (928) | (854) | (2,783) | (2,562) |  |
Amortization of Prior Service Cost | 32 | 16 | 98 | 47 |  |
Amortization of Net Loss (Gain) | 0 | 30 | 0 | 89 |  |
Net Periodic Benefit Cost | 89 | 114 | 266 | 342 |  |
Plan Contributions During the Period | 0 | 0 | 0 | 0 |  |
Estimated Future Contributions in the Current Fiscal Year | 0 |  | $ 0 |  |  |
Select Executive Retirement Plan |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Assumptions used calculating benefit obligation, interest rate to annuitize cash balance account |  |  |  |  |  | 5.76%
Defined benefit plan, amortization of service cost (in years) |  |  | 12 years 6 months |  |  |
Defined benefit plan, benefit obligation, period increase (decrease) |  |  | $ 122,797 |  |  |
Net Periodic Benefit Cost |  |  |  |  |  |
Service Cost | 20 | 143 | 59 | 428 |  |
Interest Cost (Benefit) | (157) |  |  |  |  |
Interest Cost |  | 85 | 3 | 244 |  |
Expected Return on Plan Assets | 237 | 0 | 237 | 0 |  |
Amortization of Prior Service Cost | 9 | 9 | 29 | 29 |  |
Amortization of Net Loss (Gain) | 6 | 18 | 18 | 55 |  |
Net Periodic Benefit Cost | 115 | 255 | 346 | 756 |  |
Plan Contributions During the Period | 127 | 99 | 382 | 325 |  |
Estimated Future Contributions in the Current Fiscal Year | 127 |  | 127 |  |  |
Postretirement Benefit Plans |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Assumptions used calculating benefit obligation, interest rate to annuitize cash balance account |  |  |  |  |  | 5.83%
Net Periodic Benefit Cost |  |  |  |  |  |
Service Cost | 11 | 14 | 34 | 42 |  |
Interest Cost (Benefit) | 79 |  |  |  |  |
Interest Cost |  | 82 | 239 | 249 |  |
Expected Return on Plan Assets | 0 | 0 | 0 | 0 |  |
Amortization of Prior Service Cost | 26 | 26 | 77 | 78 |  |
Amortization of Net Loss (Gain) | (84) | (88) | (253) | (265) |  |
Net Periodic Benefit Cost | 32 | 34 | 97 | 104 |  |
Plan Contributions During the Period | 31 | $ 28 | 112 | $ 75 |  |
Estimated Future Contributions in the Current Fiscal Year | $ 37 |  | $ 37 |  |  |
On or Subsequent to January 1, 2003 |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Service credits, percent of eligible salaries |  |  | 6.00% |  |  |
Prior to January 1, 2003 | Minimum |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Service credits, percent of eligible salaries |  |  | 6.00% |  |  |
Prior to January 1, 2003 | Maximum |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Service credits, percent of eligible salaries |  |  | 12.00% |  |  |

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