Pensions (Details) - Pension Plans [Member] - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Components of Net Periodic Benefit Cost [Abstract]
Service cost	$ 235	$ 212	$ 469	$ 424
Interest cost	364	411	728	822
Expected return on plan assets	(800)	(683)	(1,599)	(1,366)
Amortization of actuarial loss	93	105	185	210
Amortization of prior service credit	(3)	(3)	(6)	(6)
Rate-regulated adjustment	686	533	1,373	1,066
Net periodic pension expense	575	$ 575	1,150	$ 1,150
Employer Contributions [Abstract]
Estimated employer contributions in 2020					$ 2,300
Contributions made by employer			1,150
Estimated future contributions in 2020	$ 1,150		$ 1,150