Pension and Other Postretirement Benefits (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Pensions [Member]
Pension and other postretirement benefits expenses
Service cost	$ 1,649	$ 1,433
Interest cost	3,817	4,536
Expected return on plan assets	(7,393)	(7,078)
Amortization of prior service cost (credit)	80	103
Amortization of actuarial (gains) losses	3,339	2,158
Net periodic benefit cost	1,492	1,152
Other Postretirement Benefits [Member]
Pension and other postretirement benefits expenses
Service cost	22	19
Interest cost	264	340
Amortization of prior service cost (credit)	7	6
Amortization of actuarial (gains) losses	23	10
Net periodic benefit cost	$ 316	$ 375