Fair Value Measurements and Derivative Instruments - Fair Value of Company's Derivatives (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	Feb. 28, 2013	Aug. 31, 2012
Derivative Instruments And Hedging Activities Disclosure [Abstract]
Cash collateral due offset	$ 1.1	$ 2.6

The amount of the right to reclaim cash collateral under master netting arrangements that have not been offset against net derivative instrument positions.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 8

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=7476318&loc=d3e41678-113959

Name:	us-gaap_DerivativeCollateralRightToReclaimCash
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant