Defined Benefit Plans - Net Periodic Pension and Postretirement Benefit Costs (Details) - Pension Plans, Defined Benefit [Member] - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service costs	$ 300	$ 280
Interest costs	300	320
Expected return on plan assets	(430)	(370)
Amortization of net (gain)/loss	250	250
Net periodic benefit cost	$ 420	$ 480