Pensions and Other Postretirement Benefit Plans (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1,960	$ 1,991
Interest cost	5,507	6,110
Expected return on assets	(6,004)	(6,763)
Curtailment gain		(130)
Amortization of prior service cost/(credit)	27	28
Amortization of net actuarial loss	1,943	1,756
Net periodic benefit cost	3,433	2,992
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	183	190
Interest cost	1,660	1,832
Expected return on assets
Curtailment gain
Amortization of prior service cost/(credit)	(3,366)	(3,366)
Amortization of net actuarial loss	2,107	2,114
Net periodic benefit cost	$ 584	$ 770