Fair Value Measurements - Quantitative Information about Level 3 Fair Value Measurements (Details) - USD ($)		12 Months Ended
		Aug. 31, 2015	Aug. 31, 2014	Aug. 31, 2013
Fair Value, Inputs, Level 3 | Accrued liability for contingent crack spread payments related to purchase of noncontroling interests | Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Forward Crack Spread Margin Quotes and Management Estimates Based on Future Settlement	[1]	$ 12.99
Risk-free interest rate	[2]	0.48%
Expected life (years)	[3]	1 year
Fair Value, Inputs, Level 3 | Accrued liability for contingent crack spread payments related to purchase of noncontroling interests | Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Forward Crack Spread Margin Quotes and Management Estimates Based on Future Settlement	[1]	$ 19.67
Risk-free interest rate	[2]	0.67%
Expected life (years)	[3]	1 year 5 months 7 days
Fair Value, Inputs, Level 3 | Accrued liability for contingent crack spread payments related to purchase of noncontroling interests | Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Forward Crack Spread Margin Quotes and Management Estimates Based on Future Settlement	[1]	$ 24.33
Risk-free interest rate	[2]	0.94%
Expected life (years)	[3]	2 years
Crack Spread Contingent Payment [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Accrued liability for contingent crack spread payments related to purchase of noncontrolling interest		$ 75,982,000	$ 114,917,000	$ 134,134,000
Crack Spread Contingent Payment [Member] | NCRA [Member] | Fair Value, Inputs, Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Accrued liability for contingent crack spread payments related to purchase of noncontrolling interest		$ 75,982,000
Contractual target crack spread margin (in dollars per share)	[4]	$ 17.50
Expected volatility	[5]	159.05%

[1] Represents forward crack spread margin quotes and management estimates based on future settlement dates

[2] Represents yield curves for U.S. Treasury securities

[3] Represents the range in the number of years remaining related to each contingent payment

[4] Represents the minimum contractual threshold that would require settlement with the counterparties

[5] Represents quarterly adjusted volatility estimates derived from daily historical market data