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Stockholders' Equity - Stock Options - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expenses	$ 9,000,000.0		$ 9,000,000.0
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	$ 321,000		$ 321,000
Unrecognized compensation expense, weighted-average period	4 months 17 days
Follow On Equity Public Offering [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Issuance of common stock through Equity Distribution Agreement, net of issuance costs, shares	5,980,000
Common stock issued per share	$ 58.00		$ 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	5,400,000	$ 2,900,000	$ 10,000,000.0	$ 5,600,000
Unrecognized compensation expenses	$ 38,000,000.0		$ 38,000,000.0
Unrecognized compensation expense, weighted-average period	2 years 6 months 7 days