Share Based Compensation - Summary of Company's Share Option Activity Related to Employees, Non-Employee Members of the Board of Directors and Non-Employee Consultants (Detail) - USD ($)	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Number of options, Beginning balance	938,637	333,660
Number of options, Granted	2,334,285	611,933
Number of options, Exercised		1,288
Number of options, Expired	0	0
Number of options, Forfeited	(10,557)	(5,668)
Number of options, Ending balance	3,262,365	938,637
Weighted- average exercise price, beginning balance	$ 5.12	$ 7.72
Weighted average remaining contractual life of options outstanding	9 years 2 months 26 days	9 years 1 month 2 days
Weighted- average exercise price, granted	$ 8.63	$ 3.73
Number of options, Options exercisable	535,241	186,394
Weighted- average exercise price, exercised		$ 7.57
Weighted average remaining contractual life of options Exercisable	7 years 10 months 17 days	8 years 2 months 15 days
Weighted- average exercise price, expired	$ 0	$ 0
Weighted- average exercise price, forfeited	(5.51)	(7.72)
Weighted- average exercise price, ending balance	7.64	5.12
Weighted- average exercise price, option Exercisable	$ 5.79	$ 7.72
Aggregate Intrinsic Value	$ 6,903,313
Aggregate Intrinsic Value, Options Exercisable	$ 0	$ 0

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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 weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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Number of options or other stock instruments for which the right to exercise has lapsed under the terms of the plan agreements.

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

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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 price at which grantees could have acquired the underlying shares with respect to stock options of the plan that expired.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.

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

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