v3.8.0.1

Employee Benefit Plans - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	May 28, 2015
Maximum employee contribution percentage	90.00%
Maximum payroll deductions, percentage	10.00%
Employee purchase price floor, percentage	85.00%
Offering period (months)	12 months
Offering periods, frequency (months)	6 months
Number of purchase periods within an offering period	2
Purchase Period Months	6 months
Purchase date, frequency (months)	6 months
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized				4,000,000
In-the-money options, maximum exercise price	$ 57.39
Options in-the-money, number	400,000
Unrecognized compensation cost	$ 128.4
Restricted Stock [Member]
Weighted average fair value of options granted	$ 75.78	$ 68.16	$ 63.63
Total fair value of RSUs vested	$ 112.2	$ 95.8	$ 60.0
Restricted Stock [Member] | Minimum [Member]
Vesting period, years	3 years
Restricted Stock [Member] | Maximum [Member]
Vesting period, years	4 years
2015 Employee Stock Purchase Plan [Member]
Stock Issued During Period, Shares, Employee Stock Purchase Plans	122,857	99,192
2005 Employee Stock Purchase Plan [Member]
Stock Issued During Period, Shares, Employee Stock Purchase Plans	8,539	115,848

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- Definition

Employee purchase price floor, percentage

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The maximum exercise price for options to be considered in-the-money

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Number of months in an offering period

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- Definition

How often new offering periods commence

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Number of options that were in-the-money at the balance sheet date

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Frequency which purchasing dates occur

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- Definition

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- Definition

Maximum percentage of employee gross pay the employee may contribute to a defined contribution plan.

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- Definition

Unrecognized cost of unvested share-based compensation awards.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
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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.

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- Definition

Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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- Definition

The highest percentage of annual salary that an employee is permitted to utilize with respect to the plan.

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- Definition

The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

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- Definition

The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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Number of shares issued during the period as a result of an employee stock purchase plan.

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