Fair Value Measurements - Quantitative Information about Level 3 Fair Value Measurements (Details) - Crack Spread Contingent Payment [Member] - USD ($)		12 Months Ended
		Aug. 31, 2016	Aug. 31, 2015	Aug. 31, 2014
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Accrued liability for contingent crack spread payments related to purchase of noncontrolling interest		$ 15,051,000	$ 75,982,000	$ 114,917,000
NCRA [Member] | Fair Value, Inputs, Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Forward Crack Spread Margin Quotes and Management Estimates Based on Future Settlement		16.43
Accrued liability for contingent crack spread payments related to purchase of noncontrolling interest		$ 15,051,000
Contractual target crack spread margin (in dollars per share)	[1]	$ 17.50
Expected volatility	[2]	152.65%
Risk-free interest rate		0.94%
Expected life (years)		1 year

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

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