Short-Term Debt (Details) (USD $)	Nov. 30, 2012	Aug. 31, 2012	Nov. 30, 2011	Nov. 30, 2012 Commodity Credit Corporation (CCC)	Nov. 30, 2012 Seasonal line of credit CoBank, ACB	Nov. 02, 2012 Seasonal line of credit CoBank, ACB	Nov. 30, 2011 Seasonal line of credit CoBank, ACB	Nov. 30, 2012 Short-term line of credit Wells Fargo Bank	Nov. 30, 2012 Commercial Paper	Nov. 30, 2011 Commercial Paper	Nov. 30, 2012 Commercial Paper Minimum	Nov. 30, 2011 Commercial Paper Minimum	Nov. 30, 2012 Commercial Paper Maximum	Nov. 30, 2011 Commercial Paper Maximum
Short-term debt
Maximum borrowings				$ 183,000,000	$ 410,000,000	$ 350,000,000		$ 1,000,000
Maximum borrowings					350,000,000
Additional borrowing under line of credit, which can be utilized for either short-term or long-term borrowing purposes						50,000,000
Short-Term Debt	386,390,000	110,640,000	361,812,000						386,400,000	361,800,000
Fixed interest rate (as a percent)											0.42%	0.37%	0.58%	0.50%
Amount outstanding					3,300,000		3,300,000
Amount utilized for long-term borrowing purposes					3,300,000		9,300,000
Unused borrowing capacity					68,000,000		26,600,000
Unused borrowing capacity which can be utilized for short-term and long-term borrowings					$ 46,700,000		$ 25,600,000