Investments - National Cooperative Refinery Association Acquisition (Details) (National Cooperative Refinery Association [Member], USD $) In Millions, unless otherwise specified			9 Months Ended
May 31, 2013	Aug. 31, 2012	May 31, 2013 Growmark [Member]	May 31, 2013 MFA [Member]
Business Acquisition [Line Items]
Business Combination, Step Acquisition, First Closing, Equity Interest in Acquiree, Percentage	79.20%
Business Combination, Step Acquisition, Equity Interest in Acquiree, Percentage		74.50%
Business Combination, Step Acquisition, Amount			$ 48.0	$ 18.0

In a business combination achieved in stages, this element represents the acquisition-date percentage of equity in the acquiree held by the acquirer immediately before the acquisition date.

No definition available.

Name:	us-gaap_BusinessCombinationStepAcquisitionEquityInterestInAcquireePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant