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Stockholders' Equity - Stock Options - Additional Information (Detail) - USD ($)	3 Months Ended			9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expenses	$ 7,700,000			$ 7,700,000
Unrecognized compensation expense, weighted-average period	1 year 10 months 20 days
Proceeds from issuance of common stock				325,654,000	$ 73,276,000
Employee Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expenses	$ 107,000			107,000
Unrecognized compensation expense, weighted-average period	1 month 13 days
Follow On Equity Public Offering [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Issuance of common stock under Equity Distribution Agreement, net of issuance costs, shares		5,980,000
Common stock issued per share		$ 58.00
Proceeds from issuance of common stock		$ 325,700,000
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share-based compensation expense	$ 5,900,000		$ 2,900,000	15,900,000	$ 8,500,000
Unrecognized compensation expenses	$ 35,700,000			$ 35,700,000
Unrecognized compensation expense, weighted-average period	2 years 6 months 7 days