Derivative Financial Instruments (Schedule of Derivatives Instruments Statements of Financial Position) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Designated as hedging instrument
Amount of gain (loss) recognized in income on related hedged items	$ (2,197)	$ 4,822	$ (4,439)
Futures | Designated as hedging instrument | Commodity contract | Cost of goods sold
Amount of gain (loss) recognized in income on derivatives	4,920	5,763	3,596
Amount of gain (loss) recognized in income on related hedged items	582	1,814	(3,901)
Futures | Designated as hedging instrument | Inventory | Cost of goods sold
Amount of gain (loss) recognized in income on related hedged items	(2,779)	3,008	(538)
Futures | Not designated as hedging instrument | Commodity contract | Cost of goods sold
Amount of gain (loss) recognized in income on derivatives	$ 19,830	$ (18,784)	$ (8,450)