Derivative Financial Instruments - FV Hedges (Details) - Fair Value Hedge - Cost of sales - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Futures contracts      
Fair values of derivative financial instruments      
Amount of Gain (Loss) Recognized in Income on Derivatives $ (34,461) $ 151,344 $ 139,473
Inventories      
Fair values of derivative financial instruments      
Amount of Gain (Loss) Recognized in Income on Hedged Items $ 41,860 $ (158,987) $ (141,699)