Derivatives (Volume of Contracts Outstanding) (Details) lb in Thousands, gal in Thousands, bu in Thousands, T in Thousands	Mar. 31, 2020 lb	Mar. 31, 2020 bu	Mar. 31, 2020 T	Mar. 31, 2020 gal	Dec. 31, 2019 lb	Dec. 31, 2019 bu	Dec. 31, 2019 T	Dec. 31, 2019 gal	Mar. 31, 2019 lb	Mar. 31, 2019 bu	Mar. 31, 2019 T	Mar. 31, 2019 gal
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	6,571	1,021,217	2,223	172,922	14,873	1,055,476	2,495	300,982	6,739	1,168,112	2,713	373,930
Non-exchange Traded
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	6,571	757,422	2,010	104,752	14,873	724,330	2,263	120,448	6,739	818,315	2,508	235,452
Non-exchange Traded | Corn
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	555,782	0	0	0	552,359	0	0	0	624,612	0	0
Non-exchange Traded | Soybeans
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	33,950	0	0	0	34,912	0	0	0	42,859	0	0
Non-exchange Traded | Wheat
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	92,374	0	0	0	100,996	0	0	0	118,909	0	0
Non-exchange Traded | Oats
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	56,582	0	0	0	24,700	0	0	0	26,361	0	0
Non-exchange Traded | Ethanol
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	0	0	103,252	0	0	0	116,448	0	0	0	233,420
Non-exchange Traded | Corn oil
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	6,275	0	0	0	14,568	0	0	0	6,733	0	0	0
Non-exchange Traded | Other
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	296	18,734	2,010	1,500	305	11,363	2,263	4,000	6	5,574	2,508	2,032
Exchange Traded
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	263,795	213	68,170	0	331,146	232	180,534	0	349,797	205	138,478
Exchange Traded | Corn
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	165,295	0	0	0	221,740	0	0	0	197,210	0	0
Exchange Traded | Soybeans
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	37,875	0	0	0	39,145	0	0	0	47,860	0	0
Exchange Traded | Wheat
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	59,135	0	0	0	68,171	0	0	0	103,955	0	0
Exchange Traded | Oats
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	1,490	0	0	0	2,090	0	0	0	770	0	0
Exchange Traded | Ethanol
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	0	0	44,440	0	0	0	175,353	0	0	0	110,758
Exchange Traded | Natural Gas Liquids [Member]
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount									0	0	0	12,936
Exchange Traded | Propane
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	0	0	11,760	0	0	0	5,166	0	0	0	14,784
Exchange Traded | Other
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	0	213	11,970	0	0	232	15	0	2	205	0