Employee Benefit Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Pension Benefits
Components of net periodic benefit cost (credit):
Service cost	$ 0	$ 0	$ 0
Interest cost	12,799	13,521	9,396
Expected return on assets	(16,113)	(17,194)	(17,482)
Amortization of prior service credit	0	0	0
Recognized net actuarial loss (gain)	4,149	3,093	5,826
Net periodic benefit cost (credit), including amount capitalized	835	(580)	(2,260)
Less amount capitalized	0	0	0
Net periodic benefit cost	835	(580)	(2,260)
Other changes in plan assets and benefit obligations recognized in accumulated comprehensive loss:
Net loss (gain)	401	187	2,369
Amortization of actuarial (loss) gain	(359)	(292)	(1,310)
Amortization of prior service credit	0	0	0
Reclassification of postretirement liability adjustment from regulatory asset	0	0	5,343
Total recognized in accumulated other comprehensive loss	42	(105)	6,402
Other changes in plan assets and benefit obligations recognized in regulatory assets or liabilities:
Net loss (gain)	3,520	1,826	9,757
Amortization of actuarial (loss) gain	(3,790)	(2,801)	(5,373)
Amortization of prior service credit	0	0	0
Reclassification of postretirement liability adjustment from regulatory asset	0	0	(5,343)
Total recognized in regulatory assets or liabilities	(270)	(975)	(959)
Total recognized in net periodic benefit credit, accumulated other comprehensive loss and regulatory assets or liabilities	607	(1,660)	3,183
Other Postretirement Benefits
Components of net periodic benefit cost (credit):
Service cost	505	534	894
Interest cost	1,837	1,956	1,383
Expected return on assets	(5,315)	(5,361)	(5,277)
Amortization of prior service credit	(1,318)	(1,318)	(1,318)
Recognized net actuarial loss (gain)	(288)	(504)	(570)
Net periodic benefit cost (credit), including amount capitalized	(4,579)	(4,693)	(4,888)
Less amount capitalized	0	107	175
Net periodic benefit cost	(4,579)	(4,800)	(5,063)
Other changes in plan assets and benefit obligations recognized in accumulated comprehensive loss:
Net loss (gain)	71	(604)	(4,141)
Amortization of actuarial (loss) gain	130	108	(281)
Amortization of prior service credit	45	78	125
Reclassification of postretirement liability adjustment from regulatory asset	0	0	(992)
Total recognized in accumulated other comprehensive loss	246	(418)	(5,289)
Other changes in plan assets and benefit obligations recognized in regulatory assets or liabilities:
Net loss (gain)	(472)	(107)	11,920
Amortization of actuarial (loss) gain	158	304	500
Amortization of prior service credit	1,273	1,273	1,273
Reclassification of postretirement liability adjustment from regulatory asset	0	0	992
Total recognized in regulatory assets or liabilities	959	1,470	14,685
Total recognized in net periodic benefit credit, accumulated other comprehensive loss and regulatory assets or liabilities	$ (3,374)	$ (3,748)	$ 4,333