Pensions and Other Postretirement Benefit Plans (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2,085	$ 1,960
Interest cost	5,430	5,507
Expected return on assets	(6,702)	(6,004)
Curtailment gain	(750)
Amortization of prior service cost/(credit)	25	27
Amortization of net actuarial loss	1,665	1,943
Net periodic benefit cost	1,753	3,433
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	174	183
Interest cost	1,520	1,660
Expected return on assets
Curtailment gain
Amortization of prior service cost/(credit)	(3,366)	(3,366)
Amortization of net actuarial loss	2,217	2,107
Net periodic benefit cost	$ 545	$ 584