Fair Value Measurements - Quantitative Information about Level 3 Fair Value Measurements (Details) - May. 31, 2015 - National Cooperative Refinery Association [Member] - Fair Value, Measurement Frequency [Domain] - USD ($)		Total
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Accrued liability for contingent crack spread payments related to purchase of noncontrolling interest		$ 109,220,000
Fair Value, Inputs, Level 3 [Member] | Accrued liability for contingent crack spread payments related to purchase of noncontroling interests
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Contractual target crack spread margin (in dollars per share)	[1]	$ 17.50
Expected volatility	[2]	157.34%
Fair Value, Inputs, Level 3 [Member] | Accrued liability for contingent crack spread payments related to purchase of noncontroling interests | Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Forward crack spread margin	[3]	$ 20.70
Own credit risk	[4]	0.09%
Expected life (years)	[5]	3 months
Fair Value, Inputs, Level 3 [Member] | Accrued liability for contingent crack spread payments related to purchase of noncontroling interests | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Forward crack spread margin	[3]	$ 25.30
Own credit risk	[4]	0.94%
Expected life (years)	[5]	2 years 3 months
Fair Value, Inputs, Level 3 [Member] | Accrued liability for contingent crack spread payments related to purchase of noncontroling interests | Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Forward crack spread margin	[3]	$ 24.16
Own credit risk	[4]	0.54%
Expected life (years)	[5]	1 year 4 months 25 days

[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