Pensions and Other Postretirement Benefit Plans (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1,307	$ 1,319
Interest cost	3,671	4,049
Expected return on assets	(4,003)	(4,482)
Amortization of prior service cost/(credit)	18	19
Amortization of net actuarial loss	1,295	1,164
Net periodic benefit cost	2,288	2,069
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	122	127
Interest cost	1,107	1,221
Expected return on assets
Amortization of prior service cost/(credit)	(2,244)	(2,244)
Amortization of net actuarial loss	1,405	1,410
Net periodic benefit cost	$ 390	$ 514