Nature of the Business and Basis of Presentation - Additional Information (Detail) $ / shares in Units, $ in Thousands				1 Months Ended	3 Months Ended		12 Months Ended
	Nov. 14, 2017 USD ($) $ / shares shares	Nov. 06, 2017 USD ($) $ / shares shares	Oct. 20, 2017	Nov. 30, 2017 USD ($)	Mar. 31, 2018 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
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
Net loss					$ 10,644	$ 5,876	$ 38,700	$ 25,500	$ 10,200
Accumulated deficit					$ 107,484		$ 96,840
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
Net proceeds from issuance of common stock	$ 6,100	$ 71,600		$ 74,200
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
Share price | $ / shares	$ 14.00	$ 14.00