Derivatives Purchase and Sales Contracts Outstanding (Details) - Not Designated as Hedging Instrument [Member] t in Thousands, rail_car in Thousands, T in Thousands, MMBtu in Thousands, Bushels in Thousands, Barrels in Thousands	Aug. 31, 2017 T rail_car t Bushels MMBtu Barrels	Aug. 31, 2016 T rail_car t Bushels MMBtu Barrels
Grain and oilseed contracts [Member] | Long [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | Bushels	570,673	774,279
Grain and oilseed contracts [Member] | Short [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | Bushels	768,540	995,396
Energy products [Member] | Long [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | Barrels	15,072	14,740
Energy products [Member] | Short [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | Barrels	18,252	6,470
Processed grain and oilseed contracts [Member] | Long [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	299	541
Processed grain and oilseed contracts [Member] | Short [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	2,347	2,060
Crop nutrient contracts | Long [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	9	108
Crop nutrient contracts | Short [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	15	135
Ocean and barge freight contracts | Long [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | t	2,777	4,406
Ocean and barge freight contracts | Short [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | t	1,766	877
Rail freight contracts | Long [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | rail_car	176	205
Rail freight contracts | Short [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | rail_car	75	79
Natural gas contracts [Member] | Long [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | MMBtu	500	3,550
Natural gas contracts [Member] | Short [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | MMBtu	0	300