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Employee Benefit Plans 4 (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Union plan      
Weighted-average assumptions used to determine net periodic cost:      
Expected long-term return on plan assets 5.75% 6.00% 6.00%
Non-union plan      
Weighted-average assumptions used to determine net periodic cost:      
Expected long-term return on plan assets 4.00% 4.20% 4.20%
Pension Benefits      
Components of Net Periodic Benefits Cost:      
Service cost $ 6,316 $ 5,558 $ 4,441
Interest cost 6,833 7,880 8,527
Expected return on plan assets (12,541) (11,798) (10,374)
Amortization of prior service cost (credit) 434 435 434
Amortization of actuarial (gain) loss 3,817 1,935 1,419
Net periodic pension cost under accounting standards 4,859 4,010 4,447
Regulatory adjustment (1,277) (483) (593)
Total expense recognized, before surcharges and allocation to overhead pool $ 3,582 $ 3,527 $ 3,854
Weighted-average assumptions used to determine net periodic cost:      
Discount rate 2.55% 3.43% 4.43%
Expected long-term return on plan assets 6.00% 6.25% 6.50%
Pension Benefits | Minimum      
Weighted-average assumptions used to determine net periodic cost:      
Rate of compensation increase 3.00% 3.00% 3.00%
Pension Benefits | Maximum      
Weighted-average assumptions used to determine net periodic cost:      
Rate of compensation increase 8.00% 8.00% 8.00%
Post-Retirement Medical Benefits      
Components of Net Periodic Benefits Cost:      
Service cost $ 149 $ 171 $ 186
Interest cost 110 208 285
Expected return on plan assets (537) (510) (449)
Amortization of prior service cost (credit) 0 0 0
Amortization of actuarial (gain) loss (1,417) (977) (801)
Net periodic pension cost under accounting standards (1,695) (1,108) (779)
Regulatory adjustment 0 0 0
Total expense recognized, before surcharges and allocation to overhead pool $ (1,695) $ (1,108) $ (779)
Weighted-average assumptions used to determine net periodic cost:      
Discount rate 2.20% 3.12% 4.20%