Summary of Option Activity Under Company's 2018 Plan (Detail) - $ / shares	6 Months Ended	12 Months Ended
Jun. 30, 2021	Dec. 31, 2020
Number of Shares Underlying Outstanding Options
Number of Shares Underlying Outstanding Options, Beginning Balance	2,355,615
Number of Shares Underlying Outstanding Options, Options granted	1,157,488
Number of Shares Underlying Outstanding Options, Options exercised	(5,000)
Number of Shares Underlying Outstanding Options, Options forfeited	(270,942)
Number of Shares Underlying Outstanding Options, Options expired	(569)
Number of Shares Underlying Outstanding Options, Ending Balance	3,236,592	2,355,615
Number of Shares Underlying Outstanding Options, Exercisable - June 30, 2020	1,338,239
Weighted- Average Exercise Price
Weighted- Average Exercise Price, Beginning Balance	$ 8.59
Weighted- Average Exercise Price, Options granted	5.90
Weighted- Average Exercise Price, Options exercised	4.63
Weighted- Average Exercise Price, Options forfeited	7.12
Weighted- Average Exercise Price, Options expired	582.27
Weighted- Average Exercise Price, Ending Balance	7.66	$ 8.59
Weighted- Average Exercise Price, Exercisable - June 30, 2020	$ 9.65
Weighted-Average Remaining Contractual Term (Years)
Weighted-Average Remaining Contractual Term (Years), Outstanding Balance	8 years 2 months 12 days	8 years

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

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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 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 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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