Derivative Financial Instruments (Schedule of Derivatives Instruments Statements of Financial Position) (Details) - Commodity contract - Cost of goods sold - Futures - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Designated as hedging instrument
Amount of gain (loss) recognized in income on derivatives	$ (1,453)	$ 8,516
Amount of gain (loss) recognized in income on related hedged items	(778)	(3,389)
Not designated as hedging instrument
Amount of gain (loss) recognized in income on derivatives	(4,077)	2,756
Firm commitments | Designated as hedging instrument
Amount of gain (loss) recognized in income on related hedged items	(1,499)	(793)
Inventory | Designated as hedging instrument
Amount of gain (loss) recognized in income on related hedged items	$ 721	$ (2,596)