Employee Benefit Plans - Pension Benefits and Post-Retirement Medical Benefits Recognized on Balance Sheet (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Amounts recognized on the balance sheets:
Non-current liabilities	$ (33,636)	$ (61,365)
Pension Benefits
Amounts recognized on the balance sheets:
Non-current assets	0	0
Current liabilities	0	0
Non-current liabilities	(3,772)	(26,227)
Net amount recognized	(3,772)	(26,227)
Amounts recognized in regulatory assets consist of:
Prior service cost (credit)	1,889	2,323
Net (gain) loss	4,123	23,368
Regulatory assets (liabilities)	6,012	25,691	$ 60,473
Unfunded accrued pension cost	(2,240)	536
Net liability (asset) recognized	3,772	26,227
Changes in plan assets and benefit obligations recognized in regulatory assets (liabilities):
Regulatory asset (liability) at beginning of year	25,691	60,473
Net loss (gain)	(19,245)	(30,531)
New prior service cost	0	0
Amortization of prior service (cost) credit	(434)	(434)
Amortization of net gain (loss)	0	(3,817)
Total change in regulatory asset (liability)	(19,679)	(34,782)
Regulatory asset (liability) at end of year	6,012	25,691	60,473
Net periodic pension costs	313	4,859	$ 4,010
Change in regulatory asset (liability)	(19,679)	(34,782)
Total recognized in net periodic pension cost and regulatory asset (liability)	(19,366)	(29,923)
Additional year-end information for plans with an accumulated benefit obligation in excess of plan assets:
Projected benefit obligation	190,678	259,751
Accumulated benefit obligation	181,376	243,412
Fair value of plan assets	$ 186,906	$ 233,524
Weighted-average assumptions used to determine benefit obligations at December 31:
Discount rate	5.41%	2.89%
Pension Benefits | Minimum
Weighted-average assumptions used to determine benefit obligations at December 31:
Rate of compensation increase	3.00%	3.00%	3.00%
Pension Benefits | Maximum
Weighted-average assumptions used to determine benefit obligations at December 31:
Rate of compensation increase	8.00%	8.00%	8.00%
Post-Retirement Medical Benefits
Amounts recognized on the balance sheets:
Non-current assets	$ 9,226	$ 11,087
Current liabilities	0	0
Non-current liabilities	0	0
Net amount recognized	9,226	11,087
Amounts recognized in regulatory assets consist of:
Prior service cost (credit)	0	0
Net (gain) loss	(5,846)	(9,839)
Regulatory assets (liabilities)	(5,846)	(9,839)	$ (6,855)
Unfunded accrued pension cost	(3,380)	(1,248)
Net liability (asset) recognized	(9,226)	(11,087)
Changes in plan assets and benefit obligations recognized in regulatory assets (liabilities):
Regulatory asset (liability) at beginning of year	(9,839)	(6,855)
Net loss (gain)	2,259	(4,401)
New prior service cost	0	0
Amortization of prior service (cost) credit	0	0
Amortization of net gain (loss)	1,734	1,417
Total change in regulatory asset (liability)	3,993	(2,984)
Regulatory asset (liability) at end of year	(5,846)	(9,839)	(6,855)
Net periodic pension costs	(2,132)	(1,695)	$ (1,108)
Change in regulatory asset (liability)	3,993	(2,984)
Total recognized in net periodic pension cost and regulatory asset (liability)	1,861	(4,679)
Additional year-end information for plans with an accumulated benefit obligation in excess of plan assets:
Projected benefit obligation	2,014	2,686
Fair value of plan assets	$ 11,240	$ 13,773
Weighted-average assumptions used to determine benefit obligations at December 31:
Discount rate	5.34%	2.46%