Stock-Based Compensation - Additional Information (Detail)	9 Months Ended
Sep. 30, 2011
Options and Non Performance Based Grants
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based payment award, award vesting period	4 years
Non Performance Based Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based payment award, award vesting period	5 years
Vesting Percentage of share in year three	33.33%
Vesting Percentage of share in year four	33.33%
Vesting Percentage of share in year five	33.33%
Performance Based Shares Issued in 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based payment award, award vesting period	3 years
Percentage of shares vesting over the period	50.00%
Performance Based Shares Issued in 2011 \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of shares vesting range	150.00%
Performance Based Shares Issued in 2011 \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of shares vesting range	0.00%
Performance Based Shares Issued Prior to 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based payment award, award vesting period	5 years
Vesting Percentage of share in year three	33.33%
Vesting Percentage of share in year four	33.33%
Vesting Percentage of share in year five	33.33%
Performance Based Shares Issued Prior to 2011 \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of shares vesting range	150.00%
Performance Based Shares Issued Prior to 2011 \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of shares vesting range	0.00%
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options expiration term (in years)	10 years

Reflects the dating as to when the share-based award expires as specified in the award agreement, which may be presented in a variety of ways (for example, year, month and year, day, month and year, quarter of a year).

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- Definition

Share Based Compensation Arrangement By Share Based Payment Award Options Vesting Percentage Year Five

+ Details

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- Definition

Share Based Compensation Arrangement By Share Based Payment Award Options Vesting Percentage Year Four

+ Details

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- Definition

Share Based Compensation Arrangement By Share Based Payment Award Options Vesting Percentage Year Three

+ Details

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- Definition

Share Based Compensation Arrangement by Share based Payment Award, Vesting Percentage

+ Details

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- Definition

Vesting range of the original award based on results and a rolling three year average on return on beginning equity.

+ Details

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- Definition

Description of the period of time over which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, which may be expressed in a variety of ways (for example, in years, month and year).

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A240

-Subparagraph a

-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 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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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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