Stock-Based Compensation - Summary of Unvested RSU Award Activity (Details)	6 Months Ended
Jun. 30, 2019 $ / shares shares
Restricted Stock Units
Shares
Unvested RSUs at beginning period (in shares) \| shares	810,995
Granted (in shares) \| shares	762,350
Forfeited (in shares) \| shares	(20,251)
Vested (in shares) \| shares	(402,056)
Unvested RSUs at end period (in shares) \| shares	1,151,038
Weighted-Average Grant Date Fair Value
Unvested RSUs at beginning of period, Weighted-Average Grant Date Fair Value (in dollars per share) \| $ / shares	$ 8.83
Granted, Weighted-Average Grant Date Fair Value (in dollars per share) \| $ / shares	6.39
Forfeited, Weighted-Average Grant Date Fair Value (in dollars per share) \| $ / shares	7.52
Vested, Weighted-Average Grant Date Fair Value (in dollars per share) \| $ / shares	8.28
Unvested RSUs at end of period, Weighted-Average Grant Date Fair Value (in dollars per share) \| $ / shares	$ 7.43
Performance Stock Units
Shares
Unvested RSUs at beginning period (in shares) \| shares	252,500
Granted (in shares) \| shares	669,550
Unvested RSUs at end period (in shares) \| shares	922,050
Weighted-Average Grant Date Fair Value
Unvested RSUs at beginning of period, Weighted-Average Grant Date Fair Value (in dollars per share) \| $ / shares	$ 13.75
Granted, Weighted-Average Grant Date Fair Value (in dollars per share) \| $ / shares	9.30
Unvested RSUs at end of period, Weighted-Average Grant Date Fair Value (in dollars per share) \| $ / shares	$ 10.52

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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(3)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

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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.

+ References

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-Section 50
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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).

+ References

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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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-Publisher FASB
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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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-Publisher FASB
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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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