Share-based Compensation - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	9 Months Ended
Sep. 30, 2014	Sep. 30, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of inactive stock option plan	1
Number of active stock incentive plan	1
Minimum performance awards issued multiplier	0.00%
Maximum performance awards issued multiplier	200.00%
Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock awards granted to non-employee directors	9,150	4,912
Grant date weighted average fair value of stock awards	$ 36.07	$ 27.49
PSAs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
PSAs at target level of performance included in unvested balance	185,000
Restricted Stock Units and Performance Stock Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense	$ 5.0
Expected weighted average period of compensation expense to be recognized	1 year 10 months 24 days
Minimum [Member] \| PSAs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	2 years
Maximum [Member] \| RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Maximum [Member] \| PSAs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years

Maximum performance awards issued multiplier.

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- Definition

Minimum performance awards issued multiplier.

+ References

No definition available.

+ Details

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- Definition

Number of active stock incentive plans.

+ References

No definition available.

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- Definition

Number of inactive stock option plans.

+ References

No definition available.

+ Details

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- Definition

The number of non-vested equity-based payment instruments at a target level of performance, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

+ References

No definition available.

+ Details

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- Definition

Share based compensation arrangement by stock based payment award grant date fair value.

+ References

No definition available.

+ Details

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- Definition

Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, 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 (i)

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

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- Definition

Unrecognized cost of unvested share-based awards, other than options, awarded to employees as compensation.

+ References

No definition available.

+ Details

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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

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

The number of shares or units of entity securities issued in the transaction in which equity securities were issued to pay for goods or nonemployee services.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 50

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6406099&loc=d3e25284-112666

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(1)(iv)(1)

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

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