Stock-Based Compensation - Stock Option Activity (Detail)	12 Months Ended
Dec. 31, 2018 $ / shares shares
Options
Outstanding at December 31, 2017 \| shares	3,682,958
Granted \| shares	628,614
Exercised \| shares	(214,727)
Expired/forfeited \| shares	(73,023)
Outstanding at December 31, 2018 \| shares	4,023,822
Weighted-Average Exercise Price
Outstanding at December 31, 2017 \| $ / shares	$ 36.28
Granted \| $ / shares	63.44
Exercised \| $ / shares	22.86
Expired/forfeited \| $ / shares	59.07
Outstanding at December 31, 2018 \| $ / shares	$ 40.83

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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Net 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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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
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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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