Formation and Business of the Company (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
	Jan. 31, 2018	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Schedule of Capitalization, Equity [Line Items]
Net loss		$ 12,657	$ 5,474
Net cash used in operating activities		(11,290)	$ (5,584)
Cash, cash equivalents and investments		176,600
Accumulated deficit		$ (71,848)		$ (59,191)
IPO
Schedule of Capitalization, Equity [Line Items]
Shares issued (shares)	8,050,000
Proceeds from issuance initial public offering, net	$ 125,400
Over-Allotment Option
Schedule of Capitalization, Equity [Line Items]
Shares issued (shares)	1,050,000
Convertible Stock Converted into Shares of Common Stock
Schedule of Capitalization, Equity [Line Items]
Common shares issued upon conversion of convertible stock (shares)	9,629,405