Stock-Based Compensation and Employee Stock Purchase Program - Summary of Activity Under Stock Incentive Plans (Detail) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended
Jun. 30, 2021	Dec. 31, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Shares Subject to Outstanding, Beginning Balance	889,759
Shares Subject to Outstanding, Options granted	982,042
Shares Subject to Outstanding, Options Forfeited	(115,720)
Shares Subject to Outstanding, Options Expired	(44,936)
Shares Subject to Outstanding, Ending Balance	1,711,145
Shares Subject to Outstanding, Vested and expected to vest	1,683,195
Shares Subject to Outstanding, Exercisable	612,570
Weighted-Average Exercise Price Per Share, Outstanding Beginning Balance	$ 14.46
Weighted-Average Exercise Price Per Share, Options granted	2.88
Weighted-Average Exercise Price Per Share, Options forfeited	3.52
Weighted-Average Exercise Price Per Share, Options expired	128.45
Weighted Average Exercise Price Per Share, Outstanding Ending Balance	5.56
Weighted Average Exercise Price Per Share, Vested and expected to vest	5.58
Weighted Average Exercise Price Per Share, Exercisable	$ 9.86
Aggregate Intrinsic Value, Outstanding Balance	$ 138,915	$ 240
Aggregate Intrinsic Value, Vested and expected to vest	138,563
Aggregate Intrinsic Value, Exercisable	$ 2,690

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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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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 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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