Accumulated Other Comprehensive Loss - Reclassification out of Accumulated Other Comprehensive Loss (Details) - Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member] - Reclassification out of Accumulated Other Comprehensive Income [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Amortization of net prior service cost	$ (558)	$ (4,095)	$ (793)
Amortization of net loss	18,872	57,650	38,070
Adjustment due to effects of regulation	(16,161)	(42,187)	(33,050)
Other comprehensive (income) loss, defined benefit plan, reclassification adjustment from AOCI, before tax	2,153	11,368	4,227
Other comprehensive (income) loss, defined benefit plan, reclassification adjustment from AOCI, tax	(452)	(2,387)	(888)
Other comprehensive (income) loss, defined benefit plan, reclassification adjustment from AOCI, after tax	$ 1,701	$ 8,981	$ 3,339