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Pensions (Details) - Pension Plans [Member] - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Dec. 31, 2020
Components of Net Periodic Benefit Cost [Abstract]      
Service cost $ 271 $ 234  
Interest cost 302 364  
Expected return on plan assets (913) (799)  
Amortization of actuarial loss 121 92  
Amortization of prior service credit (3) (3)  
Rate-regulated adjustment 797 687  
Net periodic pension expense 575 $ 575  
Employer Contributions [Abstract]      
Estimated employer contributions in 2021     $ 2,300
Contributions made by employer 575    
Estimated future contributions in 2021 $ 1,725