Pensions (Details) - Pension Plans [Member] - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Components of Net Periodic Pension Cost [Abstract]
Service cost	$ 213	$ 253	$ 637	$ 761
Interest cost	412	378	1,234	1,136
Expected return on plan assets	(684)	(698)	(2,050)	(2,094)
Amortization of actuarial loss	106	102	316	305
Amortization of prior service cost	(4)	(3)	(10)	(10)
Rate-regulated adjustment	532	543	1,598	1,627
Net periodic pension expense	575	$ 575	1,725	$ 1,725
Employer Contributions [Abstract]
Estimated employer contributions in 2019					$ 2,300
Contributions made by employer			1,725
Estimated future contributions in current year	$ 575		$ 575