Stock-Based Compensation - Schedule of Fair Value of Stock Purchase Rights Granted Under 2018 Employee Stock Purchase Plan (Detail) - 2018 Employee Stock Purchase Plan [Member]	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected dividend yield	0.00%	0.00%	0.00%
Expected term	6 months	6 months	6 months 25 days
Risk-free interest rate	5.10%	1.30%	0.10%
Expected volatility	90.10%	94.90%	88.00%