Organization - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	Mar. 21, 2018	Jun. 30, 2018	Dec. 31, 2017
Class Of Stock [Line Items]
Common stock, shares authorized	400,000,000	400,000,000	153,993,227
Preferred stock, shares authorized	10,000,000	10,000,000	0
Common stock, par value	$ 0.0001	$ 0.0001	$ 0.0001
Preferred stock, par value	$ 0.0001	$ 0.0001	$ 0.0001
Cash and investments		$ 277.5
Cash, Cash Equivalents and Short-term Investments
Class Of Stock [Line Items]
Cash and investments		$ 265.7
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