Defined Benefit Plans - Net Periodic Pension and Postretirement Benefit Costs (Details) - Pension Plans, Defined Benefit [Member] - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service costs	$ 280	$ 270	$ 580	$ 550
Interest costs	290	320	590	640
Expected return on plan assets	(420)	(360)	(850)	(730)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement and Curtailment	2,500	0	2,500	0
Amortization of net (gain)/loss	240	250	490	500
Net periodic benefit cost	$ 2,890	$ 480	$ 3,310	$ 960