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Share based compensation arrangement by share based payment award value issued in 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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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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The aggregate amount of noncash, equity-based employee remuneration. This may include the value of stock or unit options, amortization of restricted stock or units, and adjustment for officers' compensation. As noncash, this element is an add back when calculating net cash generated by operating activities using the indirect method.

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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).

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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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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 an established share-based compensation plan.

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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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The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

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Net number of share options (or share units) granted during the period.

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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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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 share instruments newly issued under a share-based compensation plan.

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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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Per share or per unit amount of equity securities issued.

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Number of share options (or share units) exercised during the current period.

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Stock-Based Compensation - Additional Information (Details)					3 Months Ended		9 Months Ended
	Apr. 17, 2018 Installment shares	Nov. 29, 2017 shares	Oct. 11, 2017 shares	Jul. 11, 2016 USD ($) $ / shares shares	Sep. 30, 2018 USD ($) shares	Sep. 30, 2017 USD ($) shares	Sep. 30, 2018 USD ($) $ / shares shares	Sep. 30, 2017 USD ($) $ / shares shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Recognized stock-based compensation expense \| $							$ 2,212,000	$ 301,000
Options Issued and Outstanding
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of options exercised							0
Number of options cancelled or forfeited							0
Options granted, Number of Options							871,010
Options Issued and Outstanding \| Employees and Directors
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Option granted							863,810
Weighted-average grant date fair value of options granted \| $ / shares							$ 9.20
Expense related to options granted \| $					$ 600,000		$ 1,200,000
Unrecognized compensation expense \| $					7,400,000		$ 7,400,000
Unrecognized compensation expense, estimated weighted-average period for recognition							3 years 4 months 24 days
Options Issued and Outstanding \| Employees
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average grant date fair value of options granted \| $ / shares								$ 0.53
Expense related to options granted \| $						$ 3,000		$ 2,000
Options granted, Number of Options								64,460
Options Issued and Outstanding \| Non-employees
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Option granted							7,200
Weighted-average grant date fair value of options granted \| $ / shares							$ 12.51	$ 0.67
Expense related to options granted \| $					37,000	3,000	$ 64,000	$ 2,000
Options granted, Number of Options							7,200	46,860
Unrecognized compensation expense \| $					400,000		$ 400,000
Unrecognized compensation expense, estimated weighted-average period for recognition							2 years 10 months 13 days
Restricted Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized compensation expense, estimated weighted-average period for recognition							6 months 18 days
Shares granted	2,000						2,000
Number of quarterly installment in which restriction lapse \| Installment	4
Recognized stock-based compensation expense \| $					11,000	$ 86,000	$ 900,000	$ 300,000
Unrecognized stock-based compensation expense \| $					12,000		$ 12,000
Restricted Stock \| Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common shares issued, subject to repurchase right upon termination or cessation of service				3,772,726
Issuance price per shares \| $ / shares				$ 0.0001
Common shares issued, value \| $				$ 483
Restricted Stock Units (RSUs)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized compensation expense, estimated weighted-average period for recognition							3 years 7 months 20 days
Shares granted							24,960
Recognized stock-based compensation expense \| $					14,000		$ 20,000
Unrecognized stock-based compensation expense \| $					$ 200,000		$ 200,000
Restricted Stock Units (RSUs) \| Employees
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares granted						0	24,960	0
Weighted-average grant date fair value \| $ / shares							$ 9.03
Restricted Stock Units (RSUs) \| Non-employees
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares granted						0		0
2017 Stock Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares reserved for issuance		630,662	537,914		537,914		537,914
Number of additional shares reserved for issuance		1,866,009	630,662
2017 Stock Incentive Plan \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Terms of stock based options granted							10 years
2018 Stock Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares reserved for issuance					2,200,260		2,200,260
Percentage of additional shares added on outstanding shares							4.00%
2018 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares reserved for issuance					275,030		275,030
Number of additional shares reserved for issuance							543,926
Percentage of additional shares added on outstanding shares							1.00%