Derivatives (Details 3) lb in Thousands, gal in Thousands, bu in Thousands, T in Thousands	Jun. 30, 2017 lb	Jun. 30, 2017 bu	Jun. 30, 2017 T	Jun. 30, 2017 gal	Dec. 31, 2016 lb	Dec. 31, 2016 bu	Dec. 31, 2016 T	Dec. 31, 2016 gal	Jun. 30, 2016 lb	Jun. 30, 2016 bu	Jun. 30, 2016 T	Jun. 30, 2016 gal
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	4,658	433,265	160	261,848	9,358	391,161	110	294,345	13,800	559,552	128	167,004
Non-exchange Traded
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	4,658	264,685	100	257,018	9,358	239,451	110	216,225	13,800	338,707	128	130,464
Non-exchange Traded | Corn
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	184,197	0	0	0	175,549	0	0	0	242,269	0	0
Non-exchange Traded | Soybeans
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	31,532	0	0	0	20,592	0	0	0	52,599	0	0
Non-exchange Traded | Wheat
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	7,340	0	0	0	7,177	0	0	0	13,100	0	0
Non-exchange Traded | Oats
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	41,526	0	0	0	36,025	0	0	0	30,722	0	0
Non-exchange Traded | Ethanol
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	0	0	256,518	0	0	0	215,081	0	0	0	130,464
Non-exchange Traded | Corn Oil
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	4,658	0	0	0	9,358	0	0	0	13,800	0	0	0
Non-exchange Traded | Other
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	90	100	500	0	108	110	1,144	0	17	128	0
Exchange Traded
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	168,580	60	4,830	0	151,710	0	78,120	0	220,845	0	36,540
Exchange Traded | Corn
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	94,895	0	0	0	63,225	0	0	0	148,665	0	0
Exchange Traded | Soybeans
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	27,470	0	0	0	39,005	0	0	0	46,570	0	0
Exchange Traded | Wheat
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	43,925	0	0	0	45,360	0	0	0	22,790	0	0
Exchange Traded | Oats
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	2,290	0	0	0	4,120	0	0	0	2,820	0	0
Exchange Traded | Ethanol
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	0	0	3,990	0	0	0	78,120	0	0	0	36,540
Exchange Traded | Other
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	0	60	840