Summary of Significant Accounting Policies - Goodwill and Other Intangible Assets (Details) (USD $)	9 Months Ended
	May 31, 2014 Refineries	May 31, 2013	Aug. 31, 2013
Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 112,570,000	$ 84,166,000	$ 85,100,000
Goodwill, Acquired During Period	26,700,000
Payments to Acquire Businesses, Net of Cash Acquired	114,438,000	12,358,000
Finite-Lived Intangible Assets, Gross	115,300,000	82,100,000	81,500,000
Finite-Lived Intangible Assets, Accumulated Amortization	49,300,000	42,200,000	46,000,000
Finite-lived Intangible Assets Acquired	38,800,000	2,400,000
Amortization of Intangible Assets	7,300,000	7,400,000
Finite-Lived Intangible Assets, Amortization Expense, Next Rolling Twelve Months	9,168,000
Finite-Lived Intangible Assets, Amortization Expense, Year Two	8,828,000
Finite-Lived Intangible Assets, Amortization Expense, Year Three	7,700,000
Finite-Lived Intangible Assets, Amortization Expense, Year Four	6,050,000
Finite-Lived Intangible Assets, Amortization Expense, Year Five	3,647,000
Thereafter	30,695,000
Finite-Lived Intangible Assets, Amortization Expense, Total Future Amortization Expense	66,088,000
Number of Refineries	2
Expenditures for Major Repairs	0	53,800,000
Minimum [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	2 years
Minimum [Member] | Major Maintenance Activities Requiring Shutdown [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	2 years
Maximum [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	30 years
Maximum [Member] | Major Maintenance Activities Requiring Shutdown [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	4 years
Ag Business [Member]
Finite-Lived Intangible Assets [Line Items]
Goodwill	104,507,000	76,103,000
Ag Business [Member] | Series of Individually Immaterial Business Acquisitions [Member]
Finite-Lived Intangible Assets [Line Items]
Payments to Acquire Businesses, Gross	$ 114,400,000