Stock Based Compensation - Restricted Stock Activity Under Company's Stock Plans (Detail) - $ / shares	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding [Roll Forward]
Number, outstanding, beginning balance (in shares)	182,267
Number, granted (in shares)	0
Number, vested (in shares)	(69,714)
Number, forfeited (in shares)	(8,930)
Number, outstanding, ending balance (in shares)	103,623	182,267
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Weighted-average fair value, outstanding, beginning balance (in dollars per share)	$ 42.64
Weighted-average fair value, granted (in dollars per share)	0.00
Weighted-average fair value, vested (in dollars per share)	40.38
Weighted-average fair value, forfeited (in dollars per share)	59.77
Weighted-average fair value, outstanding, ending balance (in dollars per share)	$ 42.68	$ 42.64
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding [Roll Forward]
Number, outstanding, beginning balance (in shares)	1,046,999
Number, granted (in shares)	444,063
Number, vested (in shares)	(444,470)
Number, forfeited (in shares)	(93,014)
Number, outstanding, ending balance (in shares)	953,578	1,046,999
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Weighted-average fair value, outstanding, beginning balance (in dollars per share)	$ 42.26
Weighted-average fair value, granted (in dollars per share)	60.64
Weighted-average fair value, vested (in dollars per share)	38.36
Weighted-average fair value, forfeited (in dollars per share)	50.75
Weighted-average fair value, outstanding, ending balance (in dollars per share)	$ 51.81	$ 42.26
Restricted stock units vested for which underlying common stock to be issued (in shares)	9,641	11,058
Restricted stock units vested (in shares)	155,753	146,112

Restricted Stock Units Vested For Which Underlying Common Stock To Be Issued

No definition available.

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- Definition

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

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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.

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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).

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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).

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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.

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- Definition

The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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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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- 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.

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- Definition

Number of equity instruments other than options outstanding, including both vested and non-vested instruments.

+ References

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)(ii)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

Reference 2: 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)(i)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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No definition available.

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