Stock-Based Compensation - Summary of Nonvested Restricted Stock Awards Activity (Detail)	9 Months Ended
Sep. 30, 2019 $ / shares shares
Time-Based Restricted Stock Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Unvested shares of restricted stock outstanding at beginning of period \| shares	806,500
Restricted Stock Awards, Granted \| shares	338,900
Restricted Stock Awards, Vested \| shares	(318,500)
Restricted Stock Awards, Forfeited \| shares	(77,800)
Unvested shares of restricted stock outstanding at end of period \| shares	749,100
Unvested shares of restricted stock outstanding, Weighted Average Grant Date Fair Value, at beginning of period \| $ / shares	$ 67.54
Granted, Weighted Average Grant Date Fair Value \| $ / shares	151.10
Vested, Weighted Average Grant Date Fair Value \| $ / shares	64.06
Forfeited, Weighted Average Grant Date Fair Value \| $ / shares	85.82
Unvested shares of restricted stock outstanding, Weighted Average Grant Date Fair Value, at end of period \| $ / shares	$ 104.92
Market-Based Restricted Stock Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Restricted Stock Awards, Granted \| shares	281,000.0
Restricted Stock Awards, Vested \| shares	(280,400)
Restricted Stock Awards, Forfeited \| shares	(600)
Granted, Weighted Average Grant Date Fair Value \| $ / shares	$ 102.76
Vested, Weighted Average Grant Date Fair Value \| $ / shares	102.76
Forfeited, Weighted Average Grant Date Fair Value \| $ / shares	$ 102.57

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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-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=116856206&loc=d3e5070-113901

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- Definition

Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
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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

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
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-Paragraph 2
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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

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-Publisher FASB
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-Topic 718
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- Definition

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

+ References

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-Publisher FASB
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- Definition

Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options.

+ References

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-Publisher FASB
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- Definition

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

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-Publisher FASB
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- Definition

The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

+ References

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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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No definition available.

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