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Share based compensation arrangement by share based payment award initially authorized period start.

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Share based compensation arrangement by share based Payment award shares vested on original grant.

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Stock based compensation expense recognition 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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Aggregate number of common shares reserved for future issuance.

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Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury.

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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 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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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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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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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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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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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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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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Number of options vested.

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

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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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Stock-Based Compensation - Additional Information (Details)		3 Months Ended		9 Months Ended
	Jun. 25, 2018 shares	Sep. 30, 2018 USD ($) shares	Sep. 30, 2017 USD ($) shares	Sep. 30, 2018 USD ($) ExecutiveOfficer $ / shares shares	Sep. 30, 2017 USD ($) shares	Dec. 31, 2017 USD ($) shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of options granted				1,111,901
Maximum number of shares issued upon exercise of incentive stock options		747,477		747,477
Common stock, shares issued		19,108,221		19,108,221		948,578
Weighted average grant date fair value of options granted \| $ / shares				$ 5.77
Total intrinsic value of exercised stock options \| $				$ 237,000
Stock-based compensation expense recognized \| $		$ 430,000	$ 36,000	$ 1,544,000	$ 112,000
Stock options granted \| $		$ 0	$ 0
Early Exercise Stock Purchase Agreements
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period				36 months
Nonvested common shares outstanding		92,466		92,466		45,224
Percentage of underlying option shares whose right to purchase lapses after applicable vesting commencement date				25.00%
Right to repurchase shares underlying shares				0.0208
Other Current Liabilities \| Early Exercise Stock Purchase Agreements
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares issued upon early exercise of stock options are subject to repurchase \| $		$ 152,000		$ 152,000		$ 18,000
Stock Options Granted to Employees that Contain Performance Condition
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of options granted		0		115,657
Stock-based compensation expense recognized \| $				$ 474,000
Number of executive officers granted with purchase option \| ExecutiveOfficer				2
Number of option vested	115,657
Options vesting date				Jun. 25, 2018
Stock-based compensation expense recognition period				2018-06
Restricted Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period				4 years
Nonvested common shares outstanding		36,588		36,588		193,394
2018 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares available for future issuance		1,812,145		1,812,145
Number of shares will increase automatically through every year on specified date				--01-01
Number of shares increase automatically continuing through maximum period				beginning on January 1, 2019 and continuing through and including January 1, 2028
2018 Equity Incentive Plan \| Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Maximum number of shares available for issuance		1,600,692		1,600,692
Increase in number of shares reserved for issuance as percentage of total number of shares of capital stock outstanding on last date of preceding calendar year				5.00%
2018 Equity Incentive Plan \| Maximum [Member] \| Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Maximum number of shares available for issuance		4,000,000		4,000,000
2018 Equity Incentive Plan \| Employee options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of options granted				75,621
2018 Equity Incentive Plan \| Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of RSU granted		0	0	10,189	0
Weighted-average estimated grant-date fair value \| $ / shares				$ 17.75
Stock-based compensation expense recognized \| $				$ 181,000
2018 Equity Incentive Plan \| Incentive Stock Options \| Maximum [Member] \| Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Maximum number of shares issued upon exercise of incentive stock options		12,500,000		12,500,000
2015 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period				4 years
Options to purchase of common stock outstanding		2,102,045		2,102,045
Weighted average grant date fair value of options granted \| $ / shares				$ 4.12
Total intrinsic value of exercised stock options \| $		$ 0		$ 237,000
2015 Equity Incentive Plan \| Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options granted expiry period				10 years
2018 Employee Stock Purchase Plan \| Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares available for future issuance		200,000		200,000
Common stock, shares issued		0		0
Authorized an offering beginning period				Nov. 16, 2018
Authorized an offering ending period				May 15, 2019
2018 Employee Stock Purchase Plan \| Maximum [Member] \| Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of annual increase in number of common stock shares				1.00%
Annual increase in number of common stock shares				375,000
Option price per share of common stock at fair market value				85.00%