Summary of Significant Accounting Policies - Goodwill and Other Intangible Assets (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Feb. 29, 2016 USD ($) Refineries	Feb. 28, 2015 USD ($)	Feb. 29, 2016 USD ($) Refineries	Feb. 28, 2015 USD ($)	Aug. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Number of Refineries | Refineries	2		2
Expenditures for Major Repairs			$ 19,090	$ 7,505
Capitalized Maintenance Expense, Deferred During the Period	$ 200	$ 6,200	$ 19,100	$ 7,500
Minimum [Member] | Major Maintenance Activities Requiring Shutdown [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life			2 years
Maximum [Member] | Major Maintenance Activities Requiring Shutdown [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life			4 years
Energy [Member] | National Cooperative Refinery Association [Member]
Finite-Lived Intangible Assets [Line Items]
Business Combination, Step Acquisition, Equity Interest in Acquiree, Percentage	100.00%		100.00%		88.90%