Stockholders' Equity - Schedule of Stock Option Activity (Detail) $ / shares in Units, shares in Thousands, $ in Thousands	9 Months Ended
Sep. 30, 2018 USD ($) $ / shares shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Shares, Outstanding at December 31, 2017 \| shares	937
Number of Shares, Exercised \| shares	(267)
Number of Shares, Forfeited \| shares	(24)
Number of Shares, Outstanding at September 30, 2018 \| shares	646
Number of Shares, Exercisable at September 30, 2018 \| shares	538
Number of Shares, Vested and expected to vest at September 30, 2018 \| shares	646
Weighted - Average Exercise Price Per Share, Outstanding, Beginning balance \| $ / shares	$ 35.10
Weighted - Average Exercise Price Per Share, Exercised \| $ / shares	34.92
Weighted - Average Exercise Price Per Share, Forfeited \| $ / shares	35.39
Weighted - Average Exercise Price Per Share, Outstanding, Ending balance \| $ / shares	35.17
Weighted - Average Exercise Price Per Share, Exercisable at September 30, 2018 \| $ / shares	35.31
Weighted - Average Exercise Price Per Share, Vested and expected to vest at September 30, 2018 \| $ / shares	$ 35.17
Weighted - Average Remaining Contractual Term, Outstanding at September 30, 2018	5 years 3 months 7 days
Weighted - Average Remaining Contractual Term, Exercisable at September 30, 2018	4 years 11 months 1 day
Weighted - Average Remaining Contractual Term, Vested and expected to vest at September 30, 2018	5 years 3 months 7 days
Aggregate Intrinsic Value, Outstanding at September 30, 2018 \| $	$ 6,936
Aggregate Intrinsic Value, Exercisable at September 30, 2018 \| $	5,702
Aggregate Intrinsic Value, Vested and expected to vest at September 30, 2018 \| $	$ 6,936

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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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For presentations that combine terminations, the number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan or that expired.

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Weighted average price of options that were either forfeited or expired.

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Number of options outstanding, including both vested and non-vested options.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Number of fully vested and expected to vest exercisable options that may be converted into shares under option plan. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Amount by which current fair value of underlying stock exceeds exercise price of fully vested and expected to vest options outstanding. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Number of fully vested and expected to vest options outstanding that can be converted into shares under option plan. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Weighted-average exercise price, at which grantee can acquire shares reserved for issuance, for fully vested and expected to vest options outstanding. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average remaining contractual term for fully vested and expected to vest options outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Number of share options (or share units) exercised during the current period.

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