Condensed Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) (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, 2017	$ (6,862)	$ 0	$ 32	$ (6,894)	$ 0
Temporary equity, beginning balance, shares at Dec. 31, 2017						0	0	0
Temporary equity, beginning balance at Dec. 31, 2017						$ 0	$ 0	$ 0
Beginning balance, shares at Dec. 31, 2017		9,160,888
Issuance of Series A preferred stock for cash, net of $0.4 million in offering costs							$ 71,944
Issuance of Series A preferred stock for cash, net of $0.4 million in offering costs, shares							41,328,286
Temporary equity, issuance of stock for acquisition						$ 29,200
Temporary equity, issuance of stock for acquisition, shares						20,000,000
Issuance of stock for acquisition	2,875	$ 1	2,874
Issuance of stock for acquisition. shares		1,101,278
Issuance of Series A preferred stock to convert debt and accrued interest							$ 6,124
Issuance of Series A preferred stock to convert debt and accrued interest, shares							3,499,209
Stock-based compensation	605		605		0
Incremental vesting conditions place on previously issued common shares		(4,580,444)
Net loss	(26,037)			(26,037)	0
Ending balance at Mar. 31, 2018	(29,419)	$ 1	3,511	(32,931)	0
Temporary equity, ending balance, shares at Mar. 31, 2018						20,000,000	44,827,495	0
Temporary equity, ending balance at Mar. 31, 2018						$ 29,200	$ 78,068	$ 0
Ending balance, shares at Mar. 31, 2018		5,681,722
Beginning balance at Dec. 31, 2017	(6,862)	$ 0	32	(6,894)	0
Temporary equity, beginning balance, shares at Dec. 31, 2017						0	0	0
Temporary equity, beginning balance at Dec. 31, 2017						$ 0	$ 0	$ 0
Beginning balance, shares at Dec. 31, 2017		9,160,888
Net loss	(108,175)
Other comprehensive income (loss)	235
Ending balance at Sep. 30, 2018	(91,778)	$ 2	23,054	(115,069)	235
Temporary equity, ending balance, shares at Sep. 30, 2018						20,000,000	45,714,286	71,506,513
Temporary equity, ending balance at Sep. 30, 2018						$ 29,200	$ 79,615	$ 229,552
Ending balance, shares at Sep. 30, 2018		7,733,845
Beginning balance at Mar. 31, 2018	(29,419)	$ 1	3,511	(32,931)	0
Temporary equity, beginning balance, shares at Mar. 31, 2018						20,000,000	44,827,495	0
Temporary equity, beginning balance at Mar. 31, 2018						$ 29,200	$ 78,068	$ 0
Beginning balance, shares at Mar. 31, 2018		5,681,722
Issuance of Series A preferred stock to convert debt and accrued interest, shares							886,791
Issuance of Series A preferred stock to convert debt and accrued interest	0						$ 1,547
Vesting of restricted stock	0
Vesting of restricted stock, shares		251,542
Stock-based compensation	1,374		1,374
Stock-based compensation, shares		0
Net loss	(32,736)			(32,736)
Other comprehensive income (loss)	3				3
Ending balance at Jun. 30, 2018	(60,778)	$ 1	4,885	(65,667)	3
Temporary equity, ending balance, shares at Jun. 30, 2018						20,000,000	45,714,286	0
Temporary equity, ending balance at Jun. 30, 2018						$ 29,200	$ 79,615	$ 0
Ending balance, shares at Jun. 30, 2018		5,933,264
Issuance of Series B preferred stock for cash, net of $0.5 in offering costs	0							$ 229,552
Issuance of Series B preferred stock for cash, net of $0.5 in offering costs, shares								71,506,513
Vesting of restricted stock	1	$ 1
Vesting of restricted stock, shares		1,800,581
Stock-based compensation	18,169		18,169
Stock-based compensation, shares		0
Net loss	(49,402)			(49,402)
Other comprehensive income (loss)	232				232
Ending balance at Sep. 30, 2018	(91,778)	$ 2	23,054	(115,069)	235
Temporary equity, ending balance, shares at Sep. 30, 2018						20,000,000	45,714,286	71,506,513
Temporary equity, ending balance at Sep. 30, 2018						$ 29,200	$ 79,615	$ 229,552
Ending balance, shares at Sep. 30, 2018		7,733,845
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
Convertible preferred stock, conversion of convertible preferred stock into common stock, shares						(20,000,000)	(45,714,286)	(71,506,513)
Convertible preferred stock, conversion of convertible preferred stock into common stock						$ (29,200)	$ (79,615)	$ (229,552)
Conversion of convertible preferred stock into common stock, shares		30,493,460
Vesting of restricted stock	0
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
Temporary equity, ending balance, shares at Mar. 31, 2019						0	0	0
Temporary equity, ending balance at Mar. 31, 2019						$ 0	$ 0	$ 0
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
Conversion of convertible preferred stock into common stock, shares		30,493,460
Exercise of stock options, shares	173,712
Net loss	$ (125,609)
Other comprehensive income (loss)	389
Ending balance at Sep. 30, 2019	398,873	$ 7	678,010	(279,472)	328
Temporary equity, ending balance, shares at Sep. 30, 2019						0	0	0
Temporary equity, ending balance at Sep. 30, 2019						$ 0	$ 0	$ 0
Ending balance, shares at Sep. 30, 2019		60,984,958
Beginning balance at Mar. 31, 2019	480,260	$ 7	666,648	(186,474)	79
Temporary equity, beginning balance, shares at Mar. 31, 2019						0	0	0
Temporary equity, beginning balance at Mar. 31, 2019						$ 0	$ 0	$ 0
Beginning balance, shares at Mar. 31, 2019		60,029,470
Exercise of stock options	86		86
Exercise of stock options, shares		33,273
Vesting of restricted stock, shares		404,637
Stock-based compensation	5,140		5,140
Other additional paid-in capital	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
Temporary equity, ending balance, shares at Jun. 30, 2019						0	0	0
Temporary equity, ending balance at Jun. 30, 2019						$ 0	$ 0	$ 0
Ending balance, shares at Jun. 30, 2019		60,467,380
Exercise of stock options	369		369
Exercise of stock options, shares		112,939
Vesting of restricted stock, shares		404,639
Stock-based compensation	5,728		5,728
Net loss	(48,500)			(48,500)
Other comprehensive income (loss)	(168)				(168)
Ending balance at Sep. 30, 2019	$ 398,873	$ 7	$ 678,010	$ (279,472)	$ 328
Temporary equity, ending balance, shares at Sep. 30, 2019						0	0	0
Temporary equity, ending balance at Sep. 30, 2019						$ 0	$ 0	$ 0
Ending balance, shares at Sep. 30, 2019		60,984,958