Share-based Compensation - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	9 Months Ended
Sep. 30, 2013 OptionPlan	Sep. 30, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of inactive stock option plans	1
Number of active stock incentive plans	1
Unrecognized compensation expense	$ 4.9
Expected period of compensation expense recognition	1 year 10 months 24 days
Total intrinsic value	$ 0.1
RSUs and PSAs at target level of performance included in unvested balance	198,000
Minimum performance awards issued multiplier	0.00%
Maximum performance awards issued multiplier	200.00%
Fair market value of stock awards used in calculation of compensation expense, grant date	$ 27.49	$ 23.40
Restricted Stock Units and Performance Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period of PSAs	3 years
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period of PSAs	2 years
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period of PSAs	3 years
Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock awards granted to non-employee directors	4,912	4,807

Maximum performance awards issued multiplier.

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Minimum performance awards issued multiplier.

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- Definition

Number of active stock incentive plans.

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Number of inactive stock option plans.

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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.

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- Definition

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

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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)

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- Definition

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

+ References

No definition available.

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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

Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

+ References

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-Publisher FASB

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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

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