Stock-Based Compensation - Stock Options (Detail) - Stock Options - $ / shares shares in Thousands	6 Months Ended
Jun. 30, 2019
Shares Under Option
Outstanding at the beginning of the period (in shares)	4,630
Granted (in shares)	629
Exercised (in shares)	(876)
Cancelled (in shares)	(90)
Outstanding at the end of the period (in shares)	4,293
Exercisable as of June 30, 2019	1,714
Weighted-Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$ 37.03
Granted (in dollars per share)	157.58
Exercised (in dollars per share)	19.31
Cancelled (in dollars per share)	57.14
Outstanding at the end of the period (in dollars per share)	57.88
Exercisable as of June 30, 2019	$ 25.42

The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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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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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.

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Gross number of share options (or share units) granted during the period.

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

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

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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 price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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

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