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Stock-Based Compensation - Summary of Compensation Expense Relating to Stock Options (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Excess tax benefits from stock option activity or stock-based compensation expense recognized in cash flows from operations	$ 0	$ 0	$ 0
Excess tax benefits from stock option activity or stock-based compensation expense recognized in cash flows from financing activities	0	0	0
Employees And Non-Employee Members Of Board Of Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Compensation expense not yet recognized	$ 23,110,000
Weighted average period of compensation expense not yet recognized	2 years 6 months 14 days
Incentive Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Compensation expense	$ 11,708,000	10,300,000	8,401,000
Incentive Stock Options [Member] \| Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Compensation expense	6,765,000	5,206,000	3,919,000
Incentive Stock Options [Member] \| General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Compensation expense	4,943,000	5,094,000	4,482,000
Restricted Stock Units [Member] \| Director [Member] \| General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Compensation expense	528,000	287,000
Restricted Stock Units [Member] \| Executive Officers [Member] \| Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Compensation expense	1,432,000	604,000	476,000
Restricted Stock Units [Member] \| Executive Officers [Member] \| General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Compensation expense	$ 1,167,000	1,180,000	1,217,000
Modified Awards [Member] \| Non Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Compensation expense			$ 616,000
Shareholder Consulting Agreement [Member] \| General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Compensation expense		$ 197,000