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Retirement Benefit Plans (Details) $ in Thousands | 3 Months Ended | 6 Months Ended | 12 Months Ended |
--- | --- | --- | --- | ---
Jun. 30, 2024 USD ($) | Jun. 30, 2023 USD ($) | Jun. 30, 2024 USD ($) | Jun. 30, 2023 USD ($) | 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 | $ 380 | $ 384 | $ 846 | $ 797 |  |
Interest Cost | 595 | 519 | 1,120 | 1,049 |  |
Expected Return on Plan Assets | (923) | (851) | (1,855) | (1,708) |  |
Amortization of Prior Service Cost | 33 | 15 | 66 | 31 |  |
Amortization of Net Loss (Gain) | 0 | 23 | 0 | 59 |  |
Net Periodic Benefit Cost | 85 | 90 | 177 | 228 |  |
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 | 22 | 122 | 39 | 285 |  |
Interest Cost | 2 | 97 | 160 | 159 |  |
Expected Return on Plan Assets | 0 | 0 | 0 | 0 |  |
Amortization of Prior Service Cost | 10 | 10 | 20 | 20 |  |
Amortization of Net Loss (Gain) | (9) | 19 | 12 | 37 |  |
Net Periodic Benefit Cost | 25 | 248 | 231 | 501 |  |
Plan Contributions During the Period | 128 | 110 | 255 | 226 |  |
Estimated Future Contributions in the Current Fiscal Year | 255 |  | 255 |  |  |
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 | 8 | 10 | 23 | 28 |  |
Interest Cost | 79 | 80 | 160 | 167 |  |
Expected Return on Plan Assets | 0 | 0 | 0 | 0 |  |
Amortization of Prior Service Cost | 25 | 26 | 51 | 52 |  |
Amortization of Net Loss (Gain) | (82) | (98) | (169) | (177) |  |
Net Periodic Benefit Cost | 30 | 18 | 65 | 70 |  |
Plan Contributions During the Period | 54 | $ 20 | 81 | $ 47 |  |
Estimated Future Contributions in the Current Fiscal Year | $ 81 |  | $ 81 |  |  |
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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