Stock-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Apr. 16, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for issuance	13,808,059	12,266,171
Number of options granted	4,253,232
Aggregate intrinsic value of options exercised	$ 1,826	$ 2,077
Options Granted, Weighted-average grant-date fair value	$ 8.70	$ 12.28
Unvested restricted stock awards	599,850	1,198
Total fair value of restricted stock awards and restricted stock units vested	$ 5	$ 29
Unrecognized stock-based compensation expenses	$ 43,331
Unrecognized stock-based compensation expense, period for recognition	2 years 9 months 25 days
Additional research and development expenses		$ 417
Restricted Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unvested restricted stock awards	0
2018 Stock Option and Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of common shares that may be issued under the plan	616,300
Common shares available for future grant	2,583,736
Number of shares of common stock outstanding, increase, percentage	4.00%
Common stock reserved for issuance	2,583,736	3,877,478	3,300,000
Number of options granted	4,253,232	3,019,663
2015 Stock Option and Grant Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of common shares that may be issued under the plan	2,008,564
Common shares available for future grant	0
Option vesting period	4 years
2018 Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common shares available for future grant	1,151,010
Employee Stock Purchase Plan, description	The ESPP provides that the number of shares reserved and available for issuance will automatically increase each January 1, beginning on January 1, 2019 and each January 1 thereafter through January 1, 2028, by the least of (i) 1% of the outstanding number of shares of our common stock on the immediately preceding December 31; (ii) 1,115,700 shares or (iii) such number of shares as determined by the ESPP administrator (the “ESPP Evergreen”).
Number of common shares issued	27,580	13,425
2018 Employee Stock Purchase Plan [Member] | Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of common shares that may be issued under the plan	223,200
Number of shares of common stock outstanding, increase, percentage	1.00%
Number of common shares that may increase under the plan	1,115,700
2019 Inducement Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of common shares that may be issued under the plan	1,800,000
Common shares available for future grant	412,686
2020 Inducement Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of common shares that may be issued under the plan	1,700,000
Common shares available for future grant	1,637,000