Stockholders' Equity - Additional Information (Detail) - USD ($)						1 Months Ended	12 Months Ended
	Aug. 23, 2019	Oct. 12, 2018	Nov. 06, 2017	Nov. 01, 2017	May 11, 2016	Nov. 30, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Class Of Stock [Line Items]
Number of common stock issued upon conversion of value									$ 141,000,000
Common stock par value per share							$ 0.0001	$ 0.0001
Proceeds from common stock offering							$ 72,256,000	$ 28,547,000	$ 141,000,000
2018 Sales Agreement [Member]
Class Of Stock [Line Items]
Number of common stock issued upon conversion of shares						1,659,300	4,231,348
Common stock price per share						$ 18.00	$ 16.57
Proceeds from common stock offering						$ 28,500,000	$ 67,800,000
Percentage of gross proceeds from common stock as sales agent cash commission		3.00%
Proceeds from common stock offering							0
2018 Sales Agreement [Member] | General and Administrative Expenses [Member]
Class Of Stock [Line Items]
Legal accounting and other fees						$ 400,000	$ 200,000
2018 Sales Agreement [Member] | Maximum [Member]
Class Of Stock [Line Items]
Proceeds from common stock offering		$ 100,000,000.0
2019 Sales Agreement [Member]
Class Of Stock [Line Items]
Number of common stock issued upon conversion of shares							287,231
Common stock price per share							$ 16.48
Proceeds from common stock offering							$ 4,400,000
Percentage of gross proceeds from common stock as sales agent cash commission							3.00%
Proceeds from common stock offering							$ 145,300,000
2019 Sales Agreement [Member] | General and Administrative Expenses [Member]
Class Of Stock [Line Items]
Legal accounting and other fees							$ 200,000
2019 Sales Agreement [Member] | Maximum [Member]
Class Of Stock [Line Items]
Proceeds from common stock offering	$ 150,000,000.0
IPO [Member]
Class Of Stock [Line Items]
Number of common stock issued upon conversion of shares					6,900,000
Common stock price per share					$ 18.00
Convertible preferred stock conversion ratio							one-for-0.6465903
Conversion of convertible preferred stock into common stock					23,481,956
Private Placement [Member]
Class Of Stock [Line Items]
Number of common stock issued upon conversion of shares					3,055,554
Number of common stock issued upon conversion of value					$ 55,000,000.0
Public Offering [Member] | Underwriting Agreement [Member]
Class Of Stock [Line Items]
Number of common stock issued upon conversion of shares				6,250,000
Common stock par value per share				$ 0.0001
Proceeds from common stock offering			$ 141,000,000.0