Share-Based Compensation - Other Than Options Award Activity (Details) - USD ($) $ / shares in Units, $ in Millions	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018
RSA
Shares
Outstanding and unvested at beginning of period (in shares)	1,095,544
Granted (in shares)	0
Vested (in shares)	(1,094,336)
Forfeited (in shares)	(1,208)
Outstanding and unvested at end of period (in shares)	0
Weighted- Average Grant Date Fair Value
Outstanding and unvested at beginning of period (in dollars per share)	$ 3.02
Granted (in dollars per share)	0
Vested (in dollars per share)	3.02
Forfeited (in dollars per share)	5.38
Outstanding and unvested at end of period (in dollars per share)	$ 0
Shares surrendered for taxes (in shares)	380,564	404,466
Cost of shares surrendered for taxes	$ 3.7	$ 2.2
RSU
Shares
Outstanding and unvested at beginning of period (in shares)	1,126,681
Granted (in shares)	704,012
Vested (in shares)	(362,101)
Forfeited (in shares)	(72,824)
Outstanding and unvested at end of period (in shares)	1,395,768
Weighted- Average Grant Date Fair Value
Outstanding and unvested at beginning of period (in dollars per share)	$ 4.50
Granted (in dollars per share)	10.65
Vested (in dollars per share)	4.16
Forfeited (in dollars per share)	6.23
Outstanding and unvested at end of period (in dollars per share)	$ 7.60
Shares surrendered for taxes (in shares)	106,173	92,834
Cost of shares surrendered for taxes	$ 1.0	$ 0.7
PBRSU
Shares
Outstanding and unvested at beginning of period (in shares)	4,610,448
Granted (in shares)	1,034,534
Vested (in shares)	0
Forfeited (in shares)	(160,681)
Outstanding and unvested at end of period (in shares)	5,484,301
Weighted- Average Grant Date Fair Value
Outstanding and unvested at beginning of period (in dollars per share)	$ 4.72
Granted (in dollars per share)	10.28
Vested (in dollars per share)	0
Forfeited (in dollars per share)	6.06
Outstanding and unvested at end of period (in dollars per share)	$ 5.73
Shares surrendered for taxes (in shares)	0	0
Cost of shares surrendered for taxes	$ 0.0	$ 0.0

Amount of decrease to equity for grantee's tax withholding obligation for award under share-based payment arrangement.

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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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Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options.

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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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Number of shares used to settle grantee's tax withholding obligation for award under share-based payment arrangement.

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