Acquisitions - National Cooperative Refinery Association Acquisition (Details) (USD $)	12 Months Ended				12 Months Ended						0 Months Ended		12 Months Ended			12 Months Ended
	Aug. 31, 2013	Aug. 31, 2013 Fair Value, Inputs, Level 3 Fair Value, Measurements, Recurring	Aug. 31, 2012 Fair Value, Inputs, Level 3 Fair Value, Measurements, Recurring	Aug. 31, 2013 Accrued liability for contingent crack spread payments related to purchase of noncontroling interests Fair Value, Inputs, Level 3 Fair Value, Measurements, Recurring	Aug. 31, 2013 Accrued liability for contingent crack spread payments related to purchase of noncontroling interests Cost of Goods, Total	Aug. 31, 2012 Accrued liability for contingent crack spread payments related to purchase of noncontroling interests Cost of Goods, Total	Aug. 31, 2013 National Cooperative Refinery Association	Aug. 31, 2012 National Cooperative Refinery Association	Sep. 03, 2013 National Cooperative Refinery Association	Nov. 29, 2011 National Cooperative Refinery Association	Nov. 29, 2011 National Cooperative Refinery Association Noncontrolling Interest	Nov. 29, 2011 National Cooperative Refinery Association Parent	Aug. 31, 2013 National Cooperative Refinery Association Accrued liability for contingent crack spread payments related to purchase of noncontroling interests	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, 2013 National Cooperative Refinery Association Net Interest	Aug. 31, 2012 National Cooperative Refinery Association Net Interest	Nov. 29, 2011 National Cooperative Refinery Association Growmark contingent_payments Closings	Nov. 29, 2011 National Cooperative Refinery Association MFA contingent_payments Closings	Oct. 31, 2013 Crack Spread Contingent Payment [Member]
Business Acquisition [Line Items]
Percentage of voting interest acquired										25.571%								18.616%	6.955%
Percentage of voting interest, owned before transaction							79.20%			74.429%
Business combination, step acquisition, first closing, equity interest in acquiree, percentage									84.00%
Number of separate closings																		4	4
Aggregate base purchase price																		$ 255,500,000	$ 95,500,000
Business Combination, Step Acquisition, Future Payments Due, First Three Closings																		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							275,400,000	334,700,000
Shares Subject To Mandatory Redemption, Interest Accretion							6,700,000	6,000,000
Interest accretion					23,109,000	22,328,000
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		134,134,000	127,516,000	134,134,000
Business Acquisition, Contingent Consideration, at Fair Value													150,600,000	127,500,000	105,200,000
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability													23,100,000	22,300,000
Business Acquisition, Contingent Consideration, Potential Cash Payment																				16,500,000
Interest expense																$ 142,400,000	$ 107,200,000