Derivatives (Details 3) lb in Thousands, gal in Thousands, bu in Thousands, T in Thousands	Sep. 30, 2015 lb	Sep. 30, 2015 bu	Sep. 30, 2015 T	Sep. 30, 2015 gal	Dec. 31, 2014 lb	Dec. 31, 2014 bu	Dec. 31, 2014 T	Dec. 31, 2014 gal	Sep. 30, 2014 lb	Sep. 30, 2014 bu	Sep. 30, 2014 T	Sep. 30, 2014 gal
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	10,063	597,915	123	134,981	20,776	556,574	144	275,469	74,199	597,040	126	313,550
Non-exchange Traded
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	10,063	411,600	123	131,789	18,076	327,829	139	233,637	68,799	400,275	115	209,264
Non-exchange Traded | Corn
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	331,740	0	0	0	265,574	0	0	0	293,592	0	0
Non-exchange Traded | Soybeans
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	47,208	0	0	0	23,820	0	0	0	68,486	0	0
Non-exchange Traded | Wheat
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	12,631	0	0	0	14,967	0	0	0	11,370	0	0
Non-exchange Traded | Oats
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	19,449	0	0	0	23,440	0	0	0	26,687	0	0
Non-exchange Traded | Ethanol
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	0	0	131,789	0	0	0	233,637	0	0	0	209,264
Non-exchange Traded | Corn Oil
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	10,063	0	0	0	18,076	0	0	0	68,799	0	0	0
Non-exchange Traded | Other
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	572	123	0	0	28	139	0	0	140	115	0
Exchange Traded
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	186,315	0	3,192	2,700	228,745	5	41,832	5,400	196,765	11	104,286
Exchange Traded | Corn
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	129,810	0	0	0	159,575	0	0	0	117,175	0	0
Exchange Traded | Soybeans
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	24,860	0	0	0	31,265	0	0	0	34,760	0	0
Exchange Traded | Wheat
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	28,360	0	0	0	30,360	0	0	0	35,635	0	0
Exchange Traded | Oats
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	3,285	0	0	0	7,545	0	0	0	9,195	0	0
Exchange Traded | Ethanol
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	0	0	3,192	0	0	0	41,832	0	0	0	104,286
Exchange Traded | Bean Oil
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	0	0	0	2,700	0	0	0
Exchange Traded | Other
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	0	0	0	0	0	5	0	5,400	0	11	0