Derivatives (Volume of Contracts Outstanding) (Details) lb in Thousands, gal in Thousands, bu in Thousands, T in Thousands	Jun. 30, 2020 bu	Jun. 30, 2020 gal	Jun. 30, 2020 lb	Jun. 30, 2020 T	Dec. 31, 2019 bu	Dec. 31, 2019 gal	Dec. 31, 2019 lb	Dec. 31, 2019 T	Jun. 30, 2019 bu	Jun. 30, 2019 gal	Jun. 30, 2019 lb	Jun. 30, 2019 T
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	1,049,013	216,101	8,853	2,578	1,055,476	300,982	14,873	2,495	1,292,468	310,137	8,809	3,359
Non-exchange Traded
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	656,478	146,549	8,513	2,370	724,330	120,448	14,873	2,263	866,106	213,884	8,809	3,179
Non-exchange Traded | Corn
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	437,275	0	0	0	552,359	0	0	0	648,434	0	0	0
Non-exchange Traded | Soybeans
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	50,012	0	0	0	34,912	0	0	0	59,594	0	0	0
Non-exchange Traded | Wheat
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	95,133	0	0	0	100,996	0	0	0	93,621	0	0	0
Non-exchange Traded | Oats
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	49,053	0	0	0	24,700	0	0	0	40,582	0	0	0
Non-exchange Traded | Ethanol
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	141,549	0	0	0	116,448	0	0	0	211,352	0	0
Non-exchange Traded | Corn oil
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	0	8,098	0	0	0	14,568	0	0	0	8,809	0
Non-exchange Traded | Other
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	25,005	5,000	415	2,370	11,363	4,000	305	2,263	23,875	2,532	0	3,179
Exchange Traded
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	392,535	69,552	340	208	331,146	180,534	0	232	426,362	96,253	0	180
Exchange Traded | Corn
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	287,840	0	0	0	221,740	0	0	0	317,405	0	0	0
Exchange Traded | Soybeans
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	36,970	0	0	0	39,145	0	0	0	52,762	0	0	0
Exchange Traded | Wheat
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	67,040	0	0	0	68,171	0	0	0	55,150	0	0	0
Exchange Traded | Oats
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	685	0	0	0	2,090	0	0	0	1,045	0	0	0
Exchange Traded | Ethanol
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	27,300	0	0	0	175,353	0	0	0	82,988	0	0
Exchange Traded | Propane
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	28,602	0	0	0	5,166	0	0	0	13,230	0	0
Exchange Traded | Other
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	13,650	340	208	0	15	0	232	0	35	0	180