Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	IPO	Series A Convertible Preferred Stock	Series A Convertible Preferred Stock Series A1 Convertible Preferred Shares	Subscriptions Receivables from Preferred Stockholders	Common Stock	Common Stock IPO	Notes Receivable from Common Stockholders	Additional Paid-in Capital	Additional Paid-in Capital IPO	Accumulated Deficit	Accumulated Other Comprehensive Income
Balance at Nov. 29, 2017	$ 0		$ 0		$ 0	$ 0		$ 0	$ 0		$ 0	$ 0
Balance, Shares at Nov. 29, 2017						0
Issuance of common stock upon initial public offering, net of issuance costs	5					$ 26					(21)
Issuance of common stock upon initial public offering, net of issuance costs, Shares						26,249,993
Notes receivable from common stockholders	(5)							(5)
Net loss and comprehensive loss	(2)										(2)
Balance at Dec. 31, 2017	$ (2)					$ 26		(5)			(23)
Balance, Shares at Dec. 31, 2017	26,249,993					26,249,993
Issuance of Series A convertible preferred shares at $35.06 pershare, net of issuance costsof $635 and $84			$ 264,365	$ 34,917
Issuance of Series A convertible preferred shares at $35.06 per share, net of issuance costs of $635 and $84, Shares			7,557,990	998,225
Issuance of Series A-1 convertible preferred shares at $35.06 per share in connection with asset acquisition				$ 111,770
Issuance of Series A-1 convertible preferred shares at $35.06 per share in connection with asset acquisition, Shares				3,187,772
Proceeds received from common stockholders for issuance of founders' stock at inception	$ 5							$ 5
Subscriptions receivable from preferred stockholders	(150,000)				(150,000)
Proceeds received from preferred stockholders	150,000				$ 150,000
Issuance of common stock for early exercise of stock options	$ 5					$ 5
Issuance of common stock for early exercise of stock options, Shares	5,020,580					5,020,580
Issuance of common stock upon initial public offering, net of issuance costs		$ 343,329					$ 21			$ 343,308
Issuance of common stock upon initial public offering, net of issuance costs, Shares							20,700,000
Conversion of Series A convertible preferred stock	$ 411,052		$ (411,052)			$ 62			410,990
Conversion of Series A convertible preferred stock, Shares			(11,743,987)			61,655,922
Issuance of common stock upon conversion of convertible notes	141,410					$ 7			141,403
Issuance of common stock upon conversion of convertible stock, Shares		7,856,176				7,856,176
Adjustment for fractional shares from forward stock split	(2)								(2)
Stock-based compensation	18,566								18,566
Net loss and comprehensive loss	(211,505)										(211,505)
Net unrealized gain on available-for-sale investments, net of tax	306											306
Balance at Dec. 31, 2018	$ 703,164					$ 121			$ 914,265		$ (211,528)	$ 306
Balance, Shares at Dec. 31, 2018	121,482,671					121,482,671