Stock-Based Compensation - Summary of Stock Options Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Options Outstanding, Number of Options, Shares, Beginning Balance	1,867,747
Options Outstanding, Number of Options, Granted, Shares	131,905	0
Options Outstanding, Number of Options, Exercised, Shares	(44)
Options Outstanding, Number of Options, Cancelled, Shares	(104,746)
Options Outstanding, Number of Options, Shares, Ending Balance	1,894,862		1,867,747
Options Outstanding, Number of Options Exercisable, Shares, as of June 30, 2019	201,770
Options Outstanding, Number of Options, Vested and expected to vest, Shares as of June 30, 2019	1,894,862
Options Outstanding, Weighted Average Exercise Price, Beginning Balance	$ 9.01
Options Outstanding, Weighted Average Exercise Price, Granted	10.00
Options Outstanding, Weighted Average Exercise Price, Exercised	4.14
Options Outstanding, Weighted Average Exercise Price, Cancelled	8.23
Options Outstanding, Weighted Average Exercise Price, Ending Balance	9.14		$ 9.01
Options Outstanding, Weighted Average Exercise Price, Exercisable as of June 30, 2019	6.21
Options Outstanding, Weighted Average Exercise Price, Vested and expected to vest as of June 30, 2019	$ 9.14
Options Outstanding, Weighted Average Remaining Contractual Life (Years)	9 years 2 months 27 days		9 years 7 months 21 days
Options Outstanding, Weighted Average Remaining Contractual Life (Years), Exercisable as of June 30, 2019	7 years 6 months 21 days
Options Outstanding, Weighted Average Remaining Contractual Life (Years), Vested and expected to vest as of June 30, 2019	9 years 2 months 27 days
Options Outstanding, Aggregate Intrinsic Value	$ 596,194		$ 19,573,295
Options Outstanding, Aggregate Intrinsic Value, Exercisable as of June 30, 2019	397,416
Options Outstanding, Aggregate Intrinsic Value, Vested and expected to vest as of June 30, 2019	$ 596,194

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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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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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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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Amount by which current fair value of underlying stock exceeds exercise price of fully vested and expected to vest options outstanding. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Number of fully vested and expected to vest options outstanding that can be converted into shares under option plan. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Weighted-average exercise price, at which grantee can acquire shares reserved for issuance, for fully vested and expected to vest options outstanding. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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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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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

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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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Weighted average remaining contractual term for fully vested and expected to vest options outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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

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