Nature of the Business and Basis of Presentation - Additional Information (Detail) $ / shares in Units, $ in Thousands				3 Months Ended								12 Months Ended
	Nov. 14, 2017 USD ($) $ / shares shares	Nov. 06, 2017 USD ($) $ / shares shares	Oct. 20, 2017	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) $ / shares	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($) $ / shares	Dec. 31, 2015 USD ($)
Nature Of Business And Basis Of Presentation [Line Items]
Entity incorporation month and year												2013-12
State of incorporation												Delaware
Merger date												Jun. 30, 2017
Business combination exchange ratio												1
Share price | $ / shares								$ 0.001					$ 0.001
Net proceeds from issuance of common stock												$ 77,749
Net loss				$ (13,862)	$ (9,836)	$ (9,169)	$ (5,876)	$ (7,211)	$ (6,316)	$ (6,059)	$ (5,905)	(38,743)	$ (25,491)	$ (10,154)
Accumulated deficit				$ (96,840)				$ (45,440)				$ (96,840)	$ (45,440)
Common Stock [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Reverse stock split ratio			0.164544
Reverse stock split			one-for-6.0774
Common Stock [Member] | Initial Public Offering [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Issuance of stock, shares | shares	471,498	5,500,000										5,971,498
Share price | $ / shares	$ 14.00	$ 14.00
Net proceeds from issuance of common stock	$ 6,100	$ 71,600