Share-based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued upon the exercise of stock options	1,611,731	146,039
Share-based compensation expense	$ 4,876	$ 3,748
Shares issued under the ESPP	282,101	232,038
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period of stock options granted	10 years
Weighted-average fair value of stock option awards granted (per share)	$ 1.56	$ 0.89
Intrinsic value of stock options exercised during period	$ 2,400	$ 100
Unrecognized share-based compensation expense related to non-vested stock options	$ 5,500
Expected recognition period	2 years 10 months 1 day
Share-based compensation expense	$ 2,500	2,300
Stock Options \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Stock Options \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	4 years
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected recognition period	1 year 6 months 28 days
Share-based compensation expense	$ 2,200	$ 1,300
Weighted-average grant-date fair value of RSUs granted (per share)	$ 2.01	$ 1.83
Total vest date fair value of RSUs vested	$ 2,100	$ 3,000
Unrecognized share-based compensation expense related to non-vested RSUs	$ 500
Restricted Stock Units \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Restricted Stock Units \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	4 years
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized under the plan	5,324,000
Share-based compensation expense	$ 200	$ 100
Percentage of lower limit value of common stock	85.00%
Purchase period duration	6 months
Maximum limit of payroll deductions (percent)	10.00%
2015 Incentive Compensation Plan \| Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized under the plan	4,000,000
2018 Omnibus Incentive Compensation Plan \| Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized under the plan	18,523,000

Share-based Compensation Arrangement by Share-based Payment Award, Purchase Period

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Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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Commitment made to pay deferred cash remuneration expressed as a percentage of the individual's base salary.

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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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

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Unrecognized cost of unvested options awarded to employees as compensation.

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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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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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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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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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The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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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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Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Purchase price of common stock expressed as a percentage of its fair value.

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Number of shares issued during the period as a result of an employee stock purchase plan.

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