Stock-Based Compensation - Additional Information (Detail) $ / shares in Units, $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2018 USD ($) $ / shares shares	Sep. 30, 2018 USD ($)
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate number of shares granted to awards, share-based compensation arrangements \| shares	311,800
Weighted average exercise price of the stock options granted \| $ / shares	$ 1.10
Vesting period	4 years
Fair value of stock granted, share-based compensation arrangements	$ 0.4
Weighted average grant date fair value of the stock options granted \| $ / shares	$ 1.39
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense related to non-option	$ 1.9	$ 1.9
Options vest over vesting period
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense related to options	8.6	8.6
Performance-based Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense related to options	1.6	1.6
Compensation cost	$ 0.3	$ 1.7

Unrecognized cost of unvested share-based awards, other than options, awarded to employees as compensation.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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-Section 50
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Unrecognized cost of unvested options awarded to employees as compensation.

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- Definition

Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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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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Gross number of share options (or share units) granted during the period.

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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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Amount of capitalized and expensed compensation cost from equity-based compensation arrangements.

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Value, before forfeitures, of stock or other type of equity granted of any equity-based compensation plan other than an employee stock ownership plan (ESOP).

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