Employee Share Plans - Stock Award Activity (Detail) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
Dec. 31, 2018 USD ($) $ / shares shares
Compensation And Retirement Disclosure [Abstract]
Outstanding Beginning balance, Number of Options	3,844
Granted, Number of Options	642
Exercised, Number of Options	(864)
Expired or canceled, Number of Options	0
Outstanding Ending balance, Number of Options	3,622
Vested and exercisable Ending balance, Number of Options	2,011
Outstanding Beginning balance, Weighted Average Exercise Price Per Share \| $ / shares	$ 9.67
Granted, Weighted Average Exercise Price Per Share \| $ / shares	19.45
Exercised, Weighted Average Exercise Price Per Share \| $ / shares	7.29
Outstanding Ending balance, Weighted Average Exercise Price Per Share \| $ / shares	11.97
Vested and exercisable Ending balance, Weighted Average Exercise Price Per Share \| $ / shares	$ 9.21
Weighted Average Remaining Contractual Term, Outstanding	3 years 25 days
Weighted Average Remaining Contractual Term, Vested and exercisable at December 31, 2018	2 years 18 days
Aggregate Intrinsic Value, Outstanding Ending Balance \| $	$ 28.0
Aggregate Intrinsic Value, Vested and exercisable at December 31, 2018 \| $	$ 21.1

Share based compensation arrangement by share based payment award options vested and exercisable number.

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Share based compensation arrangement by share based payment award options vested and exercisable intrinsic value.

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Share based compensation arrangement by share based payment award options vested and exercisable weighted average remaining contractual term.

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Share based compensation arrangements by share based payment award options vested and exercised weighted average exercise price.

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- Definition

Number of options or other stock instruments for which the right to exercise has lapsed under the terms of the plan agreements.

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

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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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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
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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 per share amount at which grantees can acquire shares of common stock by exercise of options.

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

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