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Employee Postretirement Benefits - Composition of Periodic Benefit Cost (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2023 | Sep. 30, 2022 | Sep. 30, 2023 | Sep. 30, 2022
Retirement Benefits [Abstract] |  |  |  |
Net Periodic Benefit Cost (Income) | $ (1,568) | $ 1,476 | $ (4,700) | $ 4,435
Net Amount Amortized Due to the Effect of Regulation | 374 | 499 | 864 | 823
Net Periodic Benefit Cost (Income) Recognized | $ (1,194) | $ 1,975 | $ (3,836) | $ 5,258

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