Pension and Other Postretirement Benefits (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Pensions [Member]
Pension and other postretirement benefits expenses
Service cost	$ 1,433	$ 1,590
Interest cost	4,536	4,309
Expected return on plan assets	(7,078)	(7,394)
Amortization of prior service cost (credit)	103	141
Amortization of actuarial losses	2,158	2,811
Net periodic benefit cost	1,152	1,457
Other Postretirement Benefits [Member]
Pension and other postretirement benefits expenses
Service cost	19	24
Interest cost	340	344
Amortization of prior service cost (credit)	6	5
Amortization of actuarial losses	10	160
Net periodic benefit cost	$ 375	$ 533