Property, Plant and Equipment (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Abstract]
Assets under capital lease	$ 3,559	$ 3,547
Accumulated amortization capital leases	2,839	2,399
Amortization expense under capital leases	$ 424	$ 491