Summary of Significant Accounting Policies - Goodwill and Other Intangible Assets (Details) (USD $)	3 Months Ended
	Nov. 30, 2013 Refineries	Nov. 30, 2012	Aug. 31, 2013
Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 85,306,000	$ 82,904,000	$ 85,100,000
Finite-Lived Intangible Assets, Gross	85,100,000	81,700,000	81,500,000
Finite-Lived Intangible Assets, Accumulated Amortization	48,500,000	38,200,000	46,000,000
Finite-lived Intangible Assets Acquired	1,000,000
Amortization of Intangible Assets	2,300,000	2,500,000
Finite-Lived Intangible Assets, Amortization Expense, Next Rolling Twelve Months	7,511,000
Finite-Lived Intangible Assets, Amortization Expense, Year Two	6,516,000
Finite-Lived Intangible Assets, Amortization Expense, Year Three	6,066,000
Finite-Lived Intangible Assets, Amortization Expense, Year Four	4,376,000
Finite-Lived Intangible Assets, Amortization Expense, Year Five	2,043,000
Thereafter	9,398,000
Finite-Lived Intangible Assets, Net	$ 35,910,000
Number of Refineries	2
Minimum [Member] | Other Intangible Assets [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] | Other Intangible Assets [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