Stock-based Compensation - Summary of Restricted Stock and Performance Share Units Activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total fair value of shares vesting	$ 24.8	$ 9.9	$ 3.8
Restricted Stock
Beginning Balance (In Shares)	947
Granted (In Shares)	248	375	379
Vested (In Shares)	(544)
Forfeited (In Shares)	(62)
Ending Balance (In Shares)	589	947
Weighted Average Fair Value
Beginning Balance (in dollars per share)	$ 27.96
Granted (in dollars per share)	46.01	$ 29.27	$ 22.81
Vested (in dollars per share)	28.33
Forfeited (in dollars per share)	37.46
Ending Balance (in dollars per share)	$ 34.18	$ 27.96
Performance Share Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total fair value of shares vesting	$ 22.6	$ 7.9	$ 3.4
Restricted Stock
Beginning Balance (In Shares)	822
Granted (In Shares)	486
Vested (In Shares)	(51)
Forfeited (In Shares)	(458)
Ending Balance (In Shares)	799	822
Weighted Average Fair Value
Beginning Balance (in dollars per share)	$ 26.31
Granted (in dollars per share)	38.51
Vested (in dollars per share)	30.06
Forfeited (in dollars per share)	26.96
Ending Balance (in dollars per share)	$ 33.11	$ 26.31

The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section 50
-Paragraph 2
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- Definition

Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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- Definition

The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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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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The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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- Definition

Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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- Definition

The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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