Derivatives (Volume of Contracts Outstanding) (Details) lb in Thousands, gal in Thousands, bu in Thousands, T in Thousands	Sep. 30, 2020 bu	Sep. 30, 2020 gal	Sep. 30, 2020 lb	Sep. 30, 2020 T	Dec. 31, 2019 bu	Dec. 31, 2019 gal	Dec. 31, 2019 lb	Dec. 31, 2019 T	Sep. 30, 2019 bu	Sep. 30, 2019 gal	Sep. 30, 2019 lb	Sep. 30, 2019 T
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	1,234,707	158,715	62,772	2,420	1,055,476	300,982	14,873	2,495	1,258,761	421,253	5,385	3,467
Non-exchange Traded
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	811,957	100,125	62,756	2,237	724,330	120,448	14,873	2,263	842,811	262,965	5,385	3,178
Non-exchange Traded | Corn
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	527,924	0	0	0	552,359	0	0	0	653,757	0	0	0
Non-exchange Traded | Soybeans
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	121,248	0	0	0	34,912	0	0	0	46,895	0	0	0
Non-exchange Traded | Wheat
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	80,546	0	0	0	100,996	0	0	0	90,598	0	0	0
Non-exchange Traded | Oats
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	40,004	0	0	0	24,700	0	0	0	36,365	0	0	0
Non-exchange Traded | Ethanol
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	96,470	0	0	0	116,448	0	0	0	256,815	0	0
Non-exchange Traded | Corn oil
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	0	45,144	0	0	0	14,568	0	0	0	5,022	0
Non-exchange Traded | Soybean Oil
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	0	17,262	0
Non-exchange Traded | Other
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	42,235	3,655	350	2,237	11,363	4,000	305	2,263	15,196	6,150	363	3,178
Exchange Traded
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	422,750	58,590	16	183	331,146	180,534	0	232	415,950	158,288	0	289
Exchange Traded | Corn
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	250,445	0	0	0	221,740	0	0	0	280,890	0	0	0
Exchange Traded | Soybeans
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	62,785	0	0	0	39,145	0	0	0	58,980	0	0	0
Exchange Traded | Wheat
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	108,805	0	0	0	68,171	0	0	0	75,345	0	0	0
Exchange Traded | Oats
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	715	0	0	0	2,090	0	0	0	735	0	0	0
Exchange Traded | Ethanol
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	19,488	0	0	0	175,353	0	0	0	145,769	0	0
Exchange Traded | Propane
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	31,962	0	0	0	5,166	0	0	0	12,516	0	0
Exchange Traded | Other
Amounts of quantities outstanding included in commodity derivative contracts
Nonmonetary notional amount	0	7,140	16	183	0	15	0	232	0	3	0	289