Share-Based Compensation - Summary of Option Activity (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Shares (In thousands)
Outstanding (in shares)	5,477,617
Granted (in shares)	0		1,355,000
Exercised (in shares)	(2,993,709)
Forfeited or expired (in shares)	(128,121)
Outstanding (in shares)	2,355,787	5,477,617
Weighted-Average Exercise Price
Outstanding (in USD per share)	$ 9.72
Granted (in USD per share)	0.00		$ 9.81
Exercised (in USD per share)	9.69
Forfeited or expired (in USD per share)	8.84
Outstanding (in USD per share)	$ 9.81	$ 9.72
Weighted-Average Remaining Contractual Terms (Years)
Outstanding	5 years 5 months	6 years
Aggregate Intrinsic Value, options outstanding	$ 37.1
Exercisable
Shares (in shares)	1,167,789
Weighted-Average Exercise Price (in USD per share)	$ 9.81
Weighted-Average Remaining Contractual Terms (Years)	3 years 10 months
Aggregate Intrinsic Value	$ 18.4

Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable [Abstract]

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Share-based Compensation Award by Share-based Payment Award, Options, Average Remaining Contractual Term [Abstract]

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

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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

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

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