Derivative Financial Instruments (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Maximum net exposure to counterparty									$ 947
Sales	$ 52,677	$ 45,774	$ 30,680	$ 41,556	$ 41,399	$ 39,441	$ 29,142	$ 38,207	170,687	$ 148,189	$ 155,266
Other, net									343	533	$ 434
Reclassification Out Of Accumulated Other Comprehensive Income [Member]
Sales									(450)	(351)
Other, net										$ (42)
Reclassification Out Of Accumulated Other Comprehensive Income [Member] \| Unrealized Gains (Losses) on Cash Flow Hedges [Member]
Sales									$ (450)