Derivatives (Comodity Derivative Contracts Outstanding) (Details) lb in Thousands, gal in Thousands, bu in Thousands, T in Thousands	Dec. 31, 2018 lb	Dec. 31, 2018 bu	Dec. 31, 2018 T	Dec. 31, 2018 gal	Dec. 31, 2017 lb	Dec. 31, 2017 bu	Dec. 31, 2017 T	Dec. 31, 2017 gal
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	2,920	506,417	66	323,975	6,074	464,085	97	237,885
Non-exchange traded
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	2,920	313,612	66	246,863	6,074	277,095	97	197,607
Non-exchange traded | Corn
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount		250,408	0			218,391	0
Non-exchange traded | Soybeans
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	22,463	0	0	0	18,127	0	0
Non-exchange traded | Wheat
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	14,017	0	0	0	14,577	0	0
Non-exchange traded | Oats
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	26,230	0	0	0	25,953	0	0
Non-exchange traded | Ethanol
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	0	0	244,863	0	0	0	197,607
Non-exchange traded | Corn oil
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	2,920	0	0	0	6,074	0	0	0
Non-exchange traded | Other
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	494	66	2,000	0	47	97	0
Exchange traded
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	192,805	0	77,112	0	186,990	0	40,278
Exchange traded | Corn
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	130,585	0	0	0	82,835	0	0
Exchange traded | Soybeans
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	26,985	0	0	0	37,170	0	0
Exchange traded | Wheat
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	33,760	0	0	0	65,640	0	0
Exchange traded | Oats
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	1,475	0	0	0	1,345	0	0
Exchange traded | Ethanol
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	0	0	77,112	0	0	0	39,438
Exchange traded | Other
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount					0	0	0	840