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	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Amortization of net prior service cost	$ (140)	$ (200)	$ (280)	$ (400)
Amortization of net loss	1,177	1,809	2,549	3,847
Adjustment due to effects of regulation	(1,061)	(1,263)	(2,316)	(2,752)
Other comprehensive (income) loss, defined benefit plan, reclassification adjustment from AOCI, before tax	(24)	346	(47)	695
Other comprehensive (income) loss, defined benefit plan, reclassification adjustment from AOCI, tax	5	(73)	10	(146)
Other comprehensive (income) loss, defined benefit plan, reclassification adjustment from AOCI, after tax	$ (19)	$ 273	$ (37)	$ 549