Condensed Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in-Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)	Series Seed Convertible Preferred Stock	Series A Convertible Preferred Stock	Series B Convertible Preferred Stock
Beginning balance at Dec. 31, 2018	$ (120,069)	$ 2	$ 33,853	$ (153,863)	$ (61)
Temporary equity, beginning balance, shares at Dec. 31, 2018						20,000,000	45,714,286	71,506,513
Temporary equity, beginning balance at Dec. 31, 2018						$ 29,200	$ 79,615	$ 229,552
Beginning balance, shares at Dec. 31, 2018		8,051,418
Issuance of common stock in connection with a public offering,net of underwriting discounts,commissions,and offering costs	291,344	$ 2	291,342
Issuance of common stock in connection with a public offering, net of underwriting discounts, commissions, and offering costs, shares		19,837,500
Conversion of convertible preferred stock into common stock	338,367	$ 3	338,364			$ (29,200)	$ (79,615)	$ (229,552)
Convertible preferred stock, conversion of convertible preferred stock into common stock						(20,000,000)	(45,714,286)	(71,506,513)
Conversion of convertible preferred stock into common stock, shares		30,493,460
Vesting of restricted stock, shares		1,619,592
Stock-based compensation	3,089		3,089
Stock-based compensation, shares		27,500
Net loss	(32,611)			(32,611)
Other comprehensive income (loss)	140				140
Ending balance at Mar. 31, 2019	480,260	$ 7	666,648	(186,474)	79
Ending balance, shares at Mar. 31, 2019		60,029,470
Beginning balance at Dec. 31, 2018	(120,069)	$ 2	33,853	(153,863)	(61)
Temporary equity, beginning balance, shares at Dec. 31, 2018						20,000,000	45,714,286	71,506,513
Temporary equity, beginning balance at Dec. 31, 2018						$ 29,200	$ 79,615	$ 229,552
Beginning balance, shares at Dec. 31, 2018		8,051,418
Net loss	(77,109)
Other comprehensive income (loss)	557
Ending balance at Jun. 30, 2019	441,444	$ 7	671,913	(230,972)	496
Ending balance, shares at Jun. 30, 2019		60,467,380
Beginning balance at Mar. 31, 2019	480,260	$ 7	666,648	(186,474)	79
Beginning balance, shares at Mar. 31, 2019		60,029,470
Vesting of restricted stock, shares		404,637
Exercise of stock options	86		86
Exercise of stock options, shares		33,273
Stock-based compensation	5,140		5,140
Other additional paid-incapital	39		39
Net loss	(44,498)			(44,498)
Other comprehensive income (loss)	417				417
Ending balance at Jun. 30, 2019	441,444	$ 7	671,913	(230,972)	496
Ending balance, shares at Jun. 30, 2019		60,467,380
Beginning balance at Dec. 31, 2019	352,485	$ 7	686,390	(334,170)	258
Beginning balance, shares at Dec. 31, 2019		61,635,477
Vesting of restricted stock, shares		404,637
Exercise of stock options	15		15
Exercise of stock options, shares		4,309
Stock-based compensation	8,244		8,244	0
Issuance of common stock pursuant to Employee Stock Purchase Plan	556		556
Stock Issued During Period, Shares, Employee Stock Purchase Plans		49,889
Net loss	(54,074)			(54,074)
Other comprehensive income (loss)	(763)				(763)
Ending balance at Mar. 31, 2020	306,463	$ 7	695,205	(388,244)	(505)
Ending balance, shares at Mar. 31, 2020		62,094,312
Beginning balance at Dec. 31, 2019	$ 352,485	$ 7	686,390	(334,170)	258
Beginning balance, shares at Dec. 31, 2019		61,635,477
Exercise of stock options, shares	44,007
Net loss	$ (120,944)
Other comprehensive income (loss)	309
Ending balance at Jun. 30, 2020	420,324	$ 8	874,863	(455,114)	567
Ending balance, shares at Jun. 30, 2020		71,972,610
Beginning balance at Mar. 31, 2020	306,463	$ 7	695,205	(388,244)	(505)
Beginning balance, shares at Mar. 31, 2020		62,094,312
Issuance of common stock in connection with a public offering,net of underwriting discounts,commissions,and offering costs	117,094	$ 1	117,093
Issuance of common stock in connection with a public offering, net of underwriting discounts, commissions, and offering costs, shares		9,433,963
Equity component of convertible noteissuance	53,635		53,635
Equity Component Of Convertible Note Issuance, Shares		0
Debt issuance costs attributable toconvertible feature	(109)		(109)
Vesting of restricted stock			0
Vesting of restricted stock, shares		404,637
Exercise of stock options	139		139
Exercise of stock options, shares		39,698
Stock-based compensation	8,900		8,900
Stock-based compensation, shares		0
Net loss	(66,870)			(66,870)
Other comprehensive income (loss)	1,072				1,072
Ending balance at Jun. 30, 2020	$ 420,324	$ 8	$ 874,863	$ (455,114)	$ 567
Ending balance, shares at Jun. 30, 2020		71,972,610