Summary of Significant Accounting Policies - Goodwill and Other Intangible Assets (Details) (USD $)	3 Months Ended
	Nov. 30, 2012 Refineries	Nov. 30, 2011	Aug. 31, 2012
Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 82,904,000	$ 26,233,000	$ 81,700,000
Finite-Lived Intangible Assets, Gross	81,700,000	75,300,000	100,600,000
Finite-Lived Intangible Assets, Accumulated Amortization	38,200,000	45,100,000	55,700,000
Finite-lived Intangible Assets Acquired	1,000,000
Amortization of Intangible Assets	2,500,000	2,700,000
Finite-Lived Intangible Assets, Amortization Expense, Next Rolling Twelve Months	10,666,000
Finite-Lived Intangible Assets, Amortization Expense, Year Two	7,078,000
Finite-Lived Intangible Assets, Amortization Expense, Year Three	6,134,000
Finite-Lived Intangible Assets, Amortization Expense, Year Four	5,875,000
Finite-Lived Intangible Assets, Amortization Expense, Year Five	4,537,000
Thereafter	9,176,000
Finite-Lived Intangible Assets, Net	43,466,000
Number of Refineries	2
Capitalized Maintenance Expense, Amortization	$ 3,900,000	$ 16,600,000
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