Pensions and Other Postretirement Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 632	$ 699
Interest cost	1,794	1,820
Expected return on assets	(2,057)	(2,247)
Amortization of prior service cost/(credit)	17	8
Amortization of net actuarial loss	564	558
Net periodic benefit cost	950	838
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	47	58
Interest cost	528	507
Expected return on assets
Amortization of prior service cost/(credit)	(1,122)	(1,122)
Amortization of net actuarial loss	557	739
Net periodic benefit cost	$ 10	$ 182