Equity Compensation - Summary of Information Related to PSUs (Detail) - PSU $ / shares in Units, $ in Thousands	9 Months Ended
Sep. 30, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($)
Number of PSUs
Beginning balance (shares) \| shares	16,350,000
Units granted (shares) \| shares	6,825,000
Units vested (shares) \| shares	0
Conversion (shares) \| shares	(22,016,250)
Ending balance (shares) \| shares	1,158,750
Weighted Average Fair Value
Beginning balance (usd per share) \| $ / shares	$ 1.41
Units granted (usd per share) \| $ / shares	1.88
Conversion (usd per share) \| $ / shares	0.00
Units vested (usd per share) \| $ / shares	0.00
Ending balance (usd per share) \| $ / shares	$ 30.95
Total Fair Value ($ in thousands)
Units outstanding \| $	$ 35,864	$ 23,054
PSUs granted \| $	12,810
PSUs vested \| $	0
Conversion \| $	$ 0
Conversion ratio	0.05

Conversion of Stock, Share Conversion Ratio

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- Definition

Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Granted Fair Value

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Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Converted

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Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Converted in Period

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Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Converted Fair Value

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- Definition

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).

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
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- Definition

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

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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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Intrinsic value of equity-based compensation awards outstanding. Excludes stock and unit options.

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Intrinsic value of equity-based compensation awards vested. Excludes stock and unit options.

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