Pensions and Other Postretirement Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 651	$ 650
Interest cost	1,828	1,994
Expected return on assets	(1,993)	(2,207)
Amortization of prior service cost/(credit)	9	9
Amortization of net actuarial loss	645	573
Net periodic benefit cost	1,140	1,019
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	61	63
Interest cost	553	611
Expected return on assets
Amortization of prior service cost/(credit)	(1,122)	(1,122)
Amortization of net actuarial loss	702	705
Net periodic benefit cost	$ 194	$ 257