Acquisitions - National Cooperative Refinery Association Acquisition (Details) (USD $)	12 Months Ended			12 Months Ended	3 Months Ended	9 Months Ended			0 Months Ended		9 Months Ended		12 Months Ended
	Aug. 31, 2012	Aug. 31, 2012 Fair Value, Inputs, Level 3 Fair Value, Measurements, Recurring	Aug. 31, 2012 Accrued liability for contingent crack spread payments related to purchase of noncontroling interests Fair Value, Inputs, Level 3 Fair Value, Measurements, Recurring	Aug. 31, 2012 Accrued liability for contingent crack spread payments related to purchase of noncontroling interests Cost of Goods, Total	Aug. 31, 2012 Mandatorily redeemable noncontrolling interests Net Interest	Aug. 31, 2012 National Cooperative Refinery Association	Nov. 29, 2011 National Cooperative Refinery Association	Nov. 28, 2011 National Cooperative Refinery Association	Nov. 29, 2011 National Cooperative Refinery Association Noncontrolling Interest	Nov. 29, 2011 National Cooperative Refinery Association Parent	Aug. 31, 2012 National Cooperative Refinery Association Accrued liability for contingent crack spread payments related to purchase of noncontroling interests	Nov. 29, 2011 National Cooperative Refinery Association Accrued liability for contingent crack spread payments related to purchase of noncontroling interests	Aug. 31, 2012 National Cooperative Refinery Association Net Interest	Nov. 30, 2011 National Cooperative Refinery Association Growmark	Nov. 29, 2011 National Cooperative Refinery Association Growmark Closings contingent_payments	Nov. 29, 2011 National Cooperative Refinery Association MFA Closings contingent_payments
Business Acquisition [Line Items]
Percentage of voting interest acquired							25.571%								18.616%	6.955%
Percentage of voting interest, owned before transaction								74.429%
Business combination, step acquisition, first closing, equity interest in acquiree, percentage						79.20%
Number of separate closings															4	4
Aggregate base purchase price															$ 255,500,000	$ 95,500,000
Aggregate base purchase price, amount paid at the first closing														48,000,000		18,000,000
Aggregate base purchase price, amount paid at the second closing															48,000,000	95,500,000
Aggregate base purchase price, amount paid at the third closing															48,000,000	95,500,000
Aggregate base purchase price, amount paid at the final closing															111,400,000	41,600,000
Number of purchase price payments															2	2
Shares subject to mandatory redemption settlement terms amount						334,700,000
Shares Subject To Mandatory Redemption, Interest Accretion						6,000,000
Interest accretion				22,328,000	(6,031,000)
Noncontrolling interests reclassified to a liability	433,864,000								337,100,000	96,700,000
Accrued liability for contingent crack spread payments related to purchase of noncontrolling interest		127,516,000	127,516,000								127,500,000	105,200,000
Contingent Liability, Change in Fair Value											22,300,000
Interest expense													$ 107,200,000