Aggregate number of common shares reserved for future issuance.

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Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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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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Number of additional shares authorized for issuance under share-based payment arrangement.

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Number of shares authorized for issuance under share-based payment arrangement.

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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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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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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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- Definition

Maximum number of shares that may be issued in accordance with the plan as a proportion of outstanding capital stock.

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Number of shares purchased for issuance under share-based payment arrangement.

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Stock-Based Compensation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions			1 Months Ended	12 Months Ended
	Jan. 01, 2020	Oct. 17, 2018	Oct. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2027	Jul. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average fair value of options granted (in usd per share)				$ 2.62	$ 2.75
Intrinsic value of share option awards exercised				$ 1.0	$ 0.2
2018 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares of common stock that may be issued (in shares)		196,000
Percentage of outstanding stock maximum		1.00%
Additional shares available for grant to ESPP (in shares)	287,664
Common stock purchased (in shares)				0
2018 Employee Stock Purchase Plan \| Scenario, Forecast
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares of common stock that may be issued (in shares)						490,000
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense				$ 3.2
Weighted-average period expected to be recognized				2 years 8 months 12 days
2002 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Additional common stock reserved for future issuance (in shares)							800,000
Number of share grants made under the plan			0
2018 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Additional common stock reserved for future issuance (in shares)				1,221,879
Number of shares of common stock that may be issued (in shares)		3,231,626
Percentage of outstanding stock maximum		3.00%
Number of options or stock awards available for grant under the plan (in shares)		862,992
2018 Plan \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares of common stock that may be issued (in shares)		9,694,878