Derivatives (Details 3) lb in Thousands, gal in Thousands, bu in Thousands, T in Thousands	Sep. 30, 2017 lb	Sep. 30, 2017 bu	Sep. 30, 2017 T	Sep. 30, 2017 gal	Dec. 31, 2016 lb	Dec. 31, 2016 bu	Dec. 31, 2016 T	Dec. 31, 2016 gal	Sep. 30, 2016 lb	Sep. 30, 2016 bu	Sep. 30, 2016 T	Sep. 30, 2016 gal
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	5,782	533,750	110	225,251	9,358	391,161	110	294,345	7,153	507,262	251	265,952
Non-exchange Traded
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	5,782	311,850	110	201,521	9,358	239,451	110	216,225	7,153	324,107	251	191,906
Non-exchange Traded | Corn
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	222,287	0	0	0	175,549	0	0	0	226,492	0	0
Non-exchange Traded | Soybeans
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	44,463	0	0	0	20,592	0	0	0	60,614	0	0
Non-exchange Traded | Wheat
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	8,598	0	0	0	7,177	0	0	0	7,933	0	0
Non-exchange Traded | Oats
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	36,451	0	0	0	36,025	0	0	0	28,939	0	0
Non-exchange Traded | Ethanol
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount		0	0	201,521	0	0	0	215,081	0	0	0	191,906
Non-exchange Traded | Corn Oil
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	5,782	0	0	0	9,358	0	0	0	7,153	0	0	0
Non-exchange Traded | Other
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount		51	110	0	0	108	110	1,144	0	129	251	0
Exchange Traded
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	221,900	0	23,730	0	151,710	0	78,120	0	183,155	0	74,046
Exchange Traded | Corn
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	113,990	0	0	0	63,225	0	0	0	105,395	0	0
Exchange Traded | Soybeans
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	45,220	0	0	0	39,005	0	0	0	35,245	0	0
Exchange Traded | Wheat
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	61,795	0	0	0	45,360	0	0	0	39,715	0	0
Exchange Traded | Oats
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	895	0	0	0	4,120	0	0	0	2,800	0	0
Exchange Traded | Ethanol
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	0	0	22,890	0	0	0	78,120	0	0	0	74,046
Exchange Traded | Other
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	0	0	840