Derivatives (Details 3) lb in Thousands, gal in Thousands, bu in Thousands, T in Thousands	Sep. 30, 2016 lb	Sep. 30, 2016 bu	Sep. 30, 2016 T	Sep. 30, 2016 gal	Dec. 31, 2015 lb	Dec. 31, 2015 bu	Dec. 31, 2015 T	Dec. 31, 2015 gal	Sep. 30, 2015 lb	Sep. 30, 2015 bu	Sep. 30, 2015 T	Sep. 30, 2015 gal
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	7,153	507,262	251	265,952	11,532	424,761	116	140,340	10,063	597,915	123	134,981
Non-exchange Traded
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	7,153	324,107	251	191,906	11,532	269,631	116	138,660	10,063	411,600	123	131,789
Non-exchange Traded | Corn
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	226,492	0	0	0	227,248	0	0	0	331,740	0	0
Non-exchange Traded | Soybeans
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	60,614	0	0	0	13,357	0	0	0	47,208	0	0
Non-exchange Traded | Wheat
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	7,933	0	0	0	13,710	0	0	0	12,631	0	0
Non-exchange Traded | Oats
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	28,939	0	0	0	15,019	0	0	0	19,449	0	0
Non-exchange Traded | Ethanol
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	0	0	191,906	0	0	0	138,660	0	0	0	131,789
Non-exchange Traded | Corn Oil
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	7,153	0	0	0	11,532	0	0	0	10,063	0	0	0
Non-exchange Traded | Other
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	129	251	0	0	297	116	0	0	572	123	0
Exchange Traded
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	183,155	0	74,046	0	155,130	0	1,680	0	186,315	0	3,192
Exchange Traded | Corn
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	105,395	0	0	0	106,260	0	0	0	129,810	0	0
Exchange Traded | Soybeans
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	35,245	0	0	0	17,255	0	0	0	24,860	0	0
Exchange Traded | Wheat
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	39,715	0	0	0	28,135	0	0	0	28,360	0	0
Exchange Traded | Oats
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	2,800	0	0	0	3,480	0	0	0	3,285	0	0
Exchange Traded | Ethanol
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	0	0	74,046	0	0	0	840	0	0	0	3,192
Exchange Traded | Other
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount					0	0	0	840