Stock-Based Compensation - Additional Information (Detail) - shares	9 Months Ended
Sep. 30, 2015	Sep. 30, 2014
Restricted Stock Units (RSU) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
The vesting graded scale	The RSUs vest on the passage of time, generally on a graded scale over a three, four, and five-year period, or in certain instances the RSUs were issued with five year cliff vesting.
Performance Share Awards (PSAs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Cumulative performance targets	3 years
Grants under performance share awards	105,017	95,691
Stock Only Stock Appreciation Rights (SOSARs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period of stock	3 years
Vesting term	10 years

Share based compensation arrangement by share based payment award award vesting period description.

No definition available.

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- Definition

Share based compensation arrangement by share based payment award equity instruments other than options cumulative performance target period.

+ References

No definition available.

+ Details

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- Definition

Estimated period over which an employee is required to provide service in exchange for the equity-based payment award, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: 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

Period 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, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

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- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(2)(iii)(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.

+ References

No definition available.

+ Details

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