Stock-Based Compensation Plans - Summarizes Transactions of SEUs (Detail) (Stock Equivalent Units [Member], USD $)	12 Months Ended
Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding, Number of Options, Beginning balance	403,262
Exercised, Number of Options	(170,317)
Forfeited, Number of Options	(8,242)
Outstanding, Number of Options, Ending balance	286,563
Outstanding, Weighted Average Exercise Price, Beginning balance	$ 3.64
Exercised, Weighted Average Exercise Price	$ 4.70
Forfeited, Weighted Average Exercise Price	$ 5.49
Outstanding, Weighted Average Exercise Price, Ending balance	$ 3.41
Discount [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted, Number of Options	54,713
Granted, Weighted Average Exercise Price	$ 0.00
Granted, Weighted Average Grant-Date Fair Value	$ 33.84
Market Value [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted, Number of Options	7,147
Granted, Weighted Average Exercise Price	$ 46.03
Granted, Weighted Average Grant-Date Fair Value	$ 14.18

Share based compensation arrangement by share based payment award equity instruments other than options exercised.

No definition available.

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- Definition

Share based compensation arrangement by share based payment award equity instruments other than options exercised in period weighted average exercise price.

+ References

No definition available.

+ Details

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- Definition

Share based compensation arrangement by share based payment award equity instruments other than options forfeited in period weighted average exercise price.

+ References

No definition available.

+ Details

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- Definition

Share based compensation arrangement by share based payment award equity instruments other than options grants in period weighted average exercise price.

+ References

No definition available.

+ Details

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- Definition

Share based compensation arrangement by share based payment award equity instruments other than options outstanding number.

+ References

No definition available.

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- Definition

Share based compensation arrangement by share based payment award equity instruments other than options outstanding weighted average exercise price.

+ References

No definition available.

+ Details

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- Definition

The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

+ 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)(1)(iv)(3)

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

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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

The weighted average fair value at grant date for nonvested equity-based awards issued 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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