Organization - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended
	Mar. 21, 2018	Mar. 31, 2018	Mar. 31, 2019	Dec. 31, 2018
Class Of Stock [Line Items]
Common stock, shares authorized	400,000,000		400,000,000	400,000,000
Preferred stock, shares authorized	10,000,000		10,000,000	10,000,000
Common stock, par value	$ 0.0001		$ 0.0001	$ 0.0001
Preferred stock, par value	$ 0.0001		$ 0.0001	$ 0.0001
Cash and investments			$ 243.1
Cash, Cash Equivalents and Short-term Investments
Class Of Stock [Line Items]
Cash and investments			$ 241.9
Common Stock
Class Of Stock [Line Items]
Common stock issued		9,200,000
IPO
Class Of Stock [Line Items]
Common stock issued	9,200,000
Common stock offering price	$ 15.00
Net proceeds from issuance of common stock excluding underwriting costs and other offering related costs	$ 124.7
IPO | Common Stock
Class Of Stock [Line Items]
Convertible preferred stock converted into common stock	30,459,574
Overallotment
Class Of Stock [Line Items]
Common stock issued	1,200,000