Aggregate number of common shares reserved for future issuance.

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Unrecognized cost of unvested share-based compensation awards.

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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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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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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 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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Stock-Based Compensation - Additional Information (Details) - USD ($)	1 Months Ended	3 Months Ended	9 Months Ended
	Oct. 31, 2018	Sep. 30, 2018	Sep. 30, 2018	Jul. 31, 2018	Dec. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance		15,262,054	15,262,054		10,738,626
Weighted average fair value of options granted			$ 2.30
Intrinsic value of share option awards exercised			$ 27,000
Employee Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance		1,315,625	1,315,625		1,075,209
Unrecognized compensation expense		$ 600,000	$ 600,000
Weighted-average period expected to be recognized			2 years 10 months 24 days
2002 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance				800,000
Number of share grants made under the plan			260,301
Number of options or stock awards available for grant under the Plan		37,830	37,830
2002 Plan \| Employee Stock Option \| Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share based compensation, stock option vesting period		4 years
2002 Plan \| Employee Stock Option \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share based compensation, stock option vesting period		10 years
2002 Plan \| Subsequent Event
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of share grants made under the plan	0