Nature of Business - Additional Information (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Description Of Business [Line Items]
Accumulated deficit	$ (53,555)		$ (33,083)
Gross proceeds from issuance of common stock		$ 78,374
IPO [Member]
Description Of Business [Line Items]
Gross proceeds from issuance of common stock	123,200
Net proceeds from issuance of common stock	114,900
Cash, cash equivalents and marketable securities	$ 71,100