Inventories (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended					12 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Inventory, Net [Abstract]
Inventory Valuation Reserves			$ (223,833)			$ (360,138)	$ (223,833)
Lower of cost or market inventory valuation adjustment	$ 106,900	$ 103,800		$ 111,100		136,305	(108,685)	$ (291,938)
Inventory Adjustments						$ 49,600
Cost of Sales Effect of Renewable Fuels Standard	$ 25,300	$ 37,900	$ 27,300		$ 30,500		$ 33,800