Summary of Significant Accounting Policies - Purchase and Sales Contracts Outstanding (Details)	Nov. 30, 2012 t Barrels Bushels	Aug. 31, 2012 T Barrels Bushels	Nov. 30, 2011 T Bushels Barrels
Purchase Contracts
Purchase and Sales Contracts [Line Items]
Grain and oilseed - bushels	674,866,000	722,895,000	573,239,000
Energy products - barrels	7,483,000	9,047,000	8,687,000
Soy products - tons	21,000	15,000	14,000
Crop nutrients - tons	1,270,000	600,000	829,000
Ocean and barge freight - metric tons	1,288,000	1,018,000	1,101,000
Sales Contracts
Purchase and Sales Contracts [Line Items]
Grain and oilseed - bushels	1,018,510,000	1,074,535,000	825,374,000
Energy products - barrels	19,817,000	19,561,000	13,338,000
Soy products - tons	360,000	215,000	285,000
Crop nutrients - tons	1,428,000	725,000	1,122,000
Ocean and barge freight - metric tons	210,000	183,000	341,000