Derivative Financial Instruments (Schedule of Derivatives Instruments Statements of Financial Position) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Designated as hedging instrument
Amount of gain (loss) recognized in income on related hedged items	$ (970)	$ 1,462
Designated as hedging instrument | Cost of goods sold
Amount of gain (loss) recognized in income on related hedged items			$ (1,581)	$ 2,809
Designated as hedging instrument | Firm commitments | Cost of goods sold
Amount of gain (loss) recognized in income on related hedged items	(793)	662	(2,223)	1,518
Designated as hedging instrument | Inventory | Cost of goods sold
Amount of gain (loss) recognized in income on related hedged items	(177)	800	642	1,291
Futures | Designated as hedging instrument | Commodity contract | Cost of goods sold
Amount of gain (loss) recognized in income on derivatives	826	(2,825)	1,281	(4,063)
Futures | Not designated as hedging instrument | Commodity contract | Cost of goods sold
Amount of gain (loss) recognized in income on derivatives	$ (638)	$ 6,707	$ (394)	$ 13,377