Share based Compensation - RSUs and PBRSUs Summary (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Vested (in shares)	(530,035)
Stock Option Plan Amended Restated 2007 Equity Incentive Plan \| Unvested restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Non-vested units as of the beginning of the period (in shares)	2,575,100	744,400
Granted (in shares)	1,811,900	2,348,700
Vested (in shares)	(530,000)	(318,200)
Forfeited (in shares)	(145,000)	(199,800)
Non-vested units as of the end of the period (in shares)	3,712,000	2,575,100
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Non-vested units as of the beginning of the period (in dollars per share)	$ 5.85	$ 7.86
Granted (in dollars per share)	16.11	5.69
Vested (in dollars per share)	6.01	9.23
Forfeited (in dollars per share)	9.65	6.24
Non-vested units as of the end of the period (in dollars per share)	$ 10.59	$ 5.85
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract]
Non-vested units, weighted average remaining years	2 years 6 months 25 days
Non-vested units, aggregate intrinsic value	$ 36.3

No definition available.

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

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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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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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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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No definition available.

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Weighted average remaining contractual term for equity-based awards excluding options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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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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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Intrinsic value of equity-based compensation awards not vested. Excludes stock and unit options.

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No definition available.

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