Cash Dividends Declared to Common Stockholders (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	9 Months Ended
May 31, 2011 October 21, 2010	May 31, 2011 January 19, 2011	May 31, 2011 April 13, 2011	May 31, 2012 October 20, 2011	May 31, 2012 January 25, 2012	May 31, 2012 April 19, 2012
Dividends Payable [Line Items]
Dividend Declaration Date	Oct. 21, 2010	Jan. 19, 2011	Apr. 13, 2011	Oct. 20, 2011	Jan. 25, 2012	Apr. 19, 2012
Dividend per Share	$ 0.07	$ 0.07	$ 0.07	$ 0.08	$ 0.08	$ 0.08
Total Cash Dividends Declared	$ 15,563	$ 15,634	$ 15,647	$ 17,379	$ 17,323	$ 17,281
Date of Record for Dividend Payment	Nov. 15, 2010	Feb. 15, 2011	May 16, 2011	Nov. 15, 2011	Feb. 16, 2012	May 15, 2012
Dividend Cash Payment Date	Dec. 01, 2010	Mar. 01, 2011	Jun. 01, 2011	Dec. 01, 2011	Mar. 01, 2012	Jun. 01, 2012

Date the declared dividend will be paid, in CCYY-MM-DD format.

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- Definition

The per share amount of a dividend declared, but not paid, as of the financial reporting date.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 50

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4304-108586

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 32

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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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- Definition

Carrying value as of the balance sheet date of dividends declared but unpaid on equity securities issued by the entity and outstanding.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.15(5))

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.15(5))

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 15

-Subparagraph a

-Article 7

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 15

-Subparagraph 5

-Article 9

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- Definition

Date the dividend to be paid was declared, in CCYY-MM-DD format.

+ References

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- Definition

Date the holder must own the stock to be entitled to the dividend, in CCYY-MM-DD format.

+ References

No definition available.

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