Derivative Financial Instruments (Schedule of Derivatives Instruments Statements of Financial Position) (Details) - Futures - Cost of goods sold - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Designated as hedging instrument
Amount of gain (loss) recognized in income on derivatives	$ (153)	$ 932
Amount of gain (loss) recognized in income on related hedged items	1,034	(944)
Designated as hedging instrument | Firm commitments
Amount of gain (loss) recognized in income on related hedged items	539	(1,222)
Designated as hedging instrument | Inventory
Amount of gain (loss) recognized in income on related hedged items	495	278
Not designated as hedging instrument
Amount of gain (loss) recognized in income on derivatives	$ (4,346)	$ (872)