Pensions and Other Postretirement Benefit Plans (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1,391	$ 1,307
Interest cost	3,621	3,671
Expected return on assets	(4,470)	(4,003)
Curtailment gain	(518)
Amortization of prior service cost/(credit)	17	18
Amortization of net actuarial loss	1,110	1,295
Net periodic benefit cost	1,151	2,288
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	116	122
Interest cost	1,013	1,107
Expected return on assets
Curtailment gain
Amortization of prior service cost/(credit)	(2,244)	(2,244)
Amortization of net actuarial loss	1,478	1,405
Net periodic benefit cost	$ 363	$ 390