Stockholders' Deficit - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2019	Dec. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Options Outstanding, Options granted	1,400,528
Options Outstanding, Ending Balance	1,400,528
Weighted-Average Exercise Price, Options granted	$ 9.10
Weighted-Average Exercise Price, Ending Balance	$ 9.10
Weighted-Average Remaining Contractual Term	9 years 11 months 8 days	0 years
Weighted-Average Remaining Contractual Term, Options exercisable	0 years
Aggregate Intrinsic Value, Balance	$ 5,575

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

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Number of options outstanding, including both vested and non-vested options.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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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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Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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