Investments Investment in NCRA entity (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Nov. 30, 2013 National Cooperative Refinery Association [Member]	Nov. 30, 2012 National Cooperative Refinery Association [Member]	Aug. 31, 2013 National Cooperative Refinery Association [Member]	Oct. 31, 2013 Crack Spread Contingent Payment [Member]	Nov. 30, 2013 Contingent Liability [Member] National Cooperative Refinery Association [Member]
Entity Information [Line Items]
Business Combination, Step Acquisition, Equity Interest in Acquiree, Percentage	84.00%		79.20%
Business Combination, Step Acquisition, Amount	$ 66.0	$ 66.0
Business Acquisition, Cost of Acquired Entity, Cash Paid				16.5
Business Acquisition, Contingent Consideration, at Fair Value					$ 151.0