Notes Payable and Long-Term Debt - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	May 31, 2012 7.750% Senior Notes Due 2016	Aug. 31, 2011 7.750% Senior Notes Due 2016	Feb. 28, 2011 7.750% Senior Notes Due 2016	May 31, 2012 8.250% Senior Notes Due 2018	Aug. 31, 2011 8.250% Senior Notes Due 2018	Aug. 31, 2007 8.250% Senior Notes Due 2018	May 31, 2012 5.625% Senior Notes Due 2020	Aug. 31, 2011 5.625% Senior Notes Due 2020
Debt Disclosure [Line Items]
Senior unsecured notes	$ 312.0			$ 400.0			$ 400.0
Senior unsecured notes, terminated interest rate	7.75%	7.75%	7.75%	8.25%	8.25%	8.25%	5.625%	5.625%
Estimated fair value of senior notes	$ 351.0			$ 463.0			$ 420.5

The stated principal amount of the debt instrument at time of issuance, which may vary from the carrying amount because of unamortized premium or discount.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 55

-Paragraph 8

-URI http://asc.fasb.org/extlink&oid=6584090&loc=d3e28878-108400

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Accounting Principles Board Opinion (APB)

-Number 21

-Paragraph 16, 20

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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