Employee Benefit Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Pension Benefits
Components of net periodic benefit credit:
Service cost	$ 0	$ 0	$ 0
Interest cost	13,521	9,396	8,767
Expected return on assets	(17,194)	(17,482)	(17,548)
Amortization of prior service credit	0	0	0
Recognized net actuarial loss (gain)	3,093	5,826	7,046
Net periodic benefit credit, including amount capitalized	(580)	(2,260)	(1,735)
Less amount capitalized	0	0	0
Net periodic benefit cost	(580)	(2,260)	(1,735)
Other changes in plan assets and benefit obligations recognized in accumulated comprehensive loss:
Net (gain) loss	187	2,369	(265)
Amortization of actuarial (loss) gain	(292)	(1,310)	(1,286)
Amortization of prior service credit	0	0	0
Reclassification of postretirement liability adjustment from regulatory asset	0	5,343	0
Total recognized in accumulated other comprehensive loss	(105)	6,402	(1,551)
Other changes in plan assets and benefit obligations recognized in regulatory assets or liabilities:
Net (gain) loss	1,826	9,757	(5,116)
Amortization of actuarial (loss) gain	(2,801)	(5,373)	(6,731)
Amortization of prior service credit	0	0	0
Reclassification of postretirement liability adjustment from regulatory asset to OCI	0	(5,343)	0
Total recognized in regulatory assets or liabilities	(975)	(959)	(11,847)
Total recognized in net periodic benefit credit, accumulated other comprehensive loss and regulatory assets or liabilities	(1,660)	3,183	(15,133)
Other Postretirement Benefits
Components of net periodic benefit credit:
Service cost	534	894	1,033
Interest cost	1,956	1,383	1,370
Expected return on assets	(5,361)	(5,277)	(5,079)
Amortization of prior service credit	(1,318)	(1,318)	(1,318)
Recognized net actuarial loss (gain)	(504)	(570)	(111)
Net periodic benefit credit, including amount capitalized	(4,693)	(4,888)	(4,105)
Less amount capitalized	107	175	150
Net periodic benefit cost	(4,800)	(5,063)	(4,255)
Other changes in plan assets and benefit obligations recognized in accumulated comprehensive loss:
Net (gain) loss	(604)	(4,141)	(2,811)
Amortization of actuarial (loss) gain	108	(281)	(135)
Amortization of prior service credit	78	125	100
Reclassification of postretirement liability adjustment from regulatory asset	0	(992)	0
Total recognized in accumulated other comprehensive loss	(418)	(5,289)	(2,846)
Other changes in plan assets and benefit obligations recognized in regulatory assets or liabilities:
Net (gain) loss	(107)	11,920	(6,292)
Amortization of actuarial (loss) gain	304	500	110
Amortization of prior service credit	1,273	1,273	1,298
Reclassification of postretirement liability adjustment from regulatory asset to OCI	0	992	0
Total recognized in regulatory assets or liabilities	1,470	14,685	(4,884)
Total recognized in net periodic benefit credit, accumulated other comprehensive loss and regulatory assets or liabilities	$ (3,748)	$ 4,333	$ (11,985)