Stock-Based Compensation - Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2021	Dec. 31, 2020
Number of Shares
Beginning balance (in shares)	1,874,514
Granted (in shares)	336,750
Exercised (in shares)	(5,860)
Forfeited (in shares)	(252,513)
Ending balance (in shares)	1,952,891	1,874,514
Number of shares Options, Exercisable (in shares)	919,423
Number of shares Options, Vested and expected to vest (in shares)	1,702,001
Weighted Average Exercise Price
Beginning balance (in usd per share)	$ 12.94
Granted (in usd per share)	6.98
Exercised (in usd per share)	7.08
Forfeited (in usd per share)	15.21
Ending balance (in usd per share)	11.64	$ 12.94
Weighted average exercise price, Exercisable (in usd per share)	15.45
Weighted average exercise price, Vested and expected to vest (in usd per share)	$ 11.92
Weighted average contractual term outstanding (in years)	7 years 10 months 24 days	8 years 3 months 18 days
Weighted average contractual term outstanding, Exercisable (in years)	6 years 8 months 12 days
Weighted average contractual term outstanding, Vested and expected to vest (in years)	7 years 9 months 18 days
Aggregate intrinsic value, Beginning balance	$ 7
Aggregate intrinsic value, Ending balance	9	$ 7
Aggregate intrinsic value, exercisable	0
Aggregate intrinsic value, vested and expected to vest	$ 5

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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Period Type:	instant

- Definition

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.