Consolidated Statements of Comprehensive Income (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Statement of Comprehensive Income [Abstract]
Reclassification adjustment for loss on derivative instruments included in net income, tax	$ 0	$ 15	$ 177
Postretirement liability gains (losses) arising during the period, tax	360	(201)	3,965
Amortization of postretirement liability losses included in net periodic benefit credit, tax	145	78	597
Reclassification of postretirement liability adjustment from regulatory asset, tax	0	0	(1,086)
Net unrealized loss on available-for-sale investments arising during the period, tax	23	46	(177)
Reclassification adjustment for loss on available-for-sale investments included in net income, tax	$ 5	$ 11	$ 31