Fair Value Measurements - Quantitative Information about Level 3 Fair Value Measurements (Details) - National Cooperative Refinery Association [Member] - Fair Value, Inputs, Level 3 [Member] - Accrued liability for contingent crack spread payments related to purchase of noncontroling interests	3 Months Ended
	Nov. 30, 2015 USD ($) $ / shares
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Contractual target crack spread margin (in dollars per share) | $ / shares	$ 17.50	[1]
Expected volatility	147.48%	[2]
Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Forward crack spread margin	$ 13.21	[3]
Own credit risk	0.48%	[4]
Expected life (years)	9 months	[5]
Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Forward crack spread margin	$ 16.37	[3]
Own credit risk	0.94%	[4]
Expected life (years)	1 year 9 months	[5]
Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Forward crack spread margin	$ 14.51	[3]
Own credit risk	0.67%	[4]
Expected life (years)	1 year 1 month 25 days	[5]

[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

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

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

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