Subsequent Event - Additional Information (Detail) (USD $) In Millions, except Per Share data	3 Months Ended	9 Months Ended
Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Sep. 30, 2011 Dividend Declared
Subsequent Event [Line Items]
Quarterly dividend, value per share				$ 0.06
Quarterly dividend, date declared				Oct. 19, 2011
Quarterly dividend, date to be paid	Sep. 09, 2011	Jun. 10, 2011	Mar. 10, 2011	Dec. 09, 2011
Quarterly dividend, date of record	Aug. 22, 2011	May 20, 2011	Feb. 22, 2011	Nov. 21, 2011
Quarterly dividend, amount declared				$ 9.4

The day, month, and year (YYYY-MM-DD) that the dividend declared as of or prior to the financial reporting date will be paid in the subsequent period.

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

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- Definition

The aggregate amount of dividends declared, but not paid, as of the financial reporting date.

+ References

Reference 1: 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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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.

Reference 2: 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

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- Definition

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

+ References

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- Definition

The day, month and year (YYYY-MM-DD) that the dividend to be paid was declared.

+ References

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- Definition

The date as of when a holder must own the stock to be entitled to the dividend. The ex-dividend date is generally 3 days before the record date.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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