Employee Benefit Plans - Pension Benefits and Post-Retirement Medical Benefits Recognized on Balance Sheet (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Amounts recognized on the balance sheets:
Non-current liabilities	$ (33,816)	$ (32,652)
Pension Benefits
Amounts recognized on the balance sheets:
Non-current assets	21,677	2,342
Current liabilities	0	0
Non-current liabilities	0	0
Net amount recognized	21,677	2,342
Amounts recognized in regulatory assets (liabilities) consist of:
Prior service cost (credit)	1,020	1,454
Net loss (gain)	(19,867)	(1,899)
Regulatory assets (liabilities)	(18,847)	(445)	$ 6,012
Prefunded plan costs	(2,830)	(1,897)
Net liability (asset) recognized	(21,677)	(2,342)
Changes in plan assets and benefit obligations recognized in regulatory assets (liabilities):
Regulatory asset (liability) at beginning of year	(445)	6,012
Net loss (gain)	(17,968)	(6,023)
New prior service cost	0	0
Amortization of prior service (cost) credit	(434)	(434)
Amortization of net gain (loss)	0	0
Total change in regulatory asset (liability)	(18,402)	(6,457)
Regulatory asset (liability) at end of year	(18,847)	(445)	6,012
Net periodic pension costs	1,968	3,289	$ 313
Change in regulatory asset (liability)	(18,402)	(6,457)
Total recognized in net periodic pension cost and regulatory asset (liability)	(16,434)	(3,168)
Additional year-end information for plans with an accumulated benefit obligation in excess of plan assets:
Projected benefit obligation	195,485	202,963
Accumulated benefit obligation	186,679	192,986
Fair value of plan assets	$ 217,162	$ 205,305
Weighted-average assumptions used to determine benefit obligations at December 31:
Discount rate	5.70%	5.16%
Pension Benefits | Minimum
Weighted-average assumptions used to determine benefit obligations at December 31:
Rate of compensation increase	2.50%	2.50%	2.50%
Pension Benefits | Maximum
Weighted-average assumptions used to determine benefit obligations at December 31:
Rate of compensation increase	6.00%	6.00%	6.00%
Post-Retirement Medical Benefits
Amounts recognized on the balance sheets:
Non-current assets	$ 12,574	$ 10,862
Current liabilities	0	0
Non-current liabilities	0	0
Net amount recognized	12,574	10,862
Amounts recognized in regulatory assets (liabilities) consist of:
Prior service cost (credit)	0	0
Net loss (gain)	(6,531)	(6,272)
Regulatory assets (liabilities)	(6,531)	(6,272)	$ (5,846)
Prefunded plan costs	(6,043)	(4,590)
Net liability (asset) recognized	(12,574)	(10,862)
Changes in plan assets and benefit obligations recognized in regulatory assets (liabilities):
Regulatory asset (liability) at beginning of year	(6,272)	(5,846)
Net loss (gain)	(1,371)	(1,395)
New prior service cost	0	0
Amortization of prior service (cost) credit	0	0
Amortization of net gain (loss)	1,112	969
Total change in regulatory asset (liability)	(259)	(426)
Regulatory asset (liability) at end of year	(6,531)	(6,272)	(5,846)
Net periodic pension costs	(1,453)	(1,210)	$ (2,132)
Change in regulatory asset (liability)	(259)	(426)
Total recognized in net periodic pension cost and regulatory asset (liability)	(1,712)	(1,636)
Additional year-end information for plans with an accumulated benefit obligation in excess of plan assets:
Projected benefit obligation	1,882	1,965
Fair value of plan assets	$ 14,456	$ 12,827
Weighted-average assumptions used to determine benefit obligations at December 31:
Discount rate	5.40%	5.04%