Share-Based Compensation - Additional Information (Detail)	12 Months Ended
Dec. 31, 2017 USD ($) $ / shares shares
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Expected volatility term	5 years
Closing stock price \| $ / shares	$ 233.77
Equity Incentive Plan
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	2,091,064
Maximum aggregate number of shares that may be awarded and sold	9,528,505
Conversion ratio for awards granted	2
Conversion ratio for awards forfeited	2
Equity Incentive Plan \| Restricted stock units
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Options, exercisable period	4 years
Equity Incentive Plan \| Restricted stock units \| Lower Limit
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Options, exercisable period	3 years
Equity Incentive Plan \| Performance-based restricted stock
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Options, exercisable period	3 years
Equity Incentive Plan \| Performance-based restricted stock \| Lower Limit
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Options, exercisable period	1 year
Equity Incentive Plan \| Stock options
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Options granted under the 2006 Incentive Plan, expiration period	7 years
Options, exercisable period	4 years
Employee Stock Purchase Plan
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	1,614,399
Maximum percentage of gross compensation that participating employees may annually contribute towards ESPP	10.00%
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Amount \| $	$ 25,000
Percentage of fair market value of common stock at which employees may purchase shares under ESPP	85.00%
Number of shares issued under ESPP	122,882
Proceeds from issuance of shares under ESPP \| $	$ 18,200,000

Compensation Related Costs Share Based Payments Disclosure [Line Items]

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The cash inflow associated with the amount received from holders to acquire the entity's shares under incentive and share awards.

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Share Based Compensation Arrangement by Share Based Payment Award, Fair Value Assumptions, Historical Volatility Term

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Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Conversion Ratio

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Maximum amount the employee may contribute to a defined contribution plan.

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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.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
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Discount rate from fair value on purchase date that participants pay for shares.

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

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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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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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Price of a single share of a number of saleable stocks of a company.

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Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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

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