Derivative Financial Instruments (Schedule of Derivatives Instruments Statements of Financial Position) (Details) - Cost of goods sold - Futures - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Designated as hedging instrument
Amount of gain (loss) recognized in income on derivatives	$ 4,122	$ 826	$ 571	$ 1,281
Amount of gain (loss) recognized in income on related hedged items	(3,041)	(970)	1,174	(1,581)
Designated as hedging instrument | Firm commitments
Amount of gain (loss) recognized in income on related hedged items	(1,711)	(793)	995	(2,223)
Designated as hedging instrument | Inventory
Amount of gain (loss) recognized in income on related hedged items	(1,330)	(177)	179	642
Not designated as hedging instrument
Amount of gain (loss) recognized in income on derivatives	$ (10,566)	$ (638)	$ (12,528)	$ (394)