Consolidated Statements of Redeemable Noncontrolling Interest and Stockholders' Equity - USD ($) $ in Thousands	Total	Series D Convertible Preferred Stock	Series E Convertible Preferred Stock	Series A Convertible Preferred Stock	Redeemable Noncontrolling Interest	Convertible Preferred Stock	Convertible Preferred Stock Series D Convertible Preferred Stock	Convertible Preferred Stock Series E Convertible Preferred Stock	Convertible Preferred Stock Series A Convertible Preferred Stock	Common Stock	Common Stock Series D Convertible Preferred Stock	Additional Paid-in Capital	Additional Paid-in Capital Series D Convertible Preferred Stock	Accumulated Other Comprehensive Gain (Loss)	Accumulated Deficit	Accumulated Deficit Series A Convertible Preferred Stock
Beginning balance at Dec. 31, 2016	$ 79,696					$ 179,997				$ 0		$ 7,410		$ (86)	$ (107,625)
Beginning balance (in shares) at Dec. 31, 2016						40,181,923				13,184,214
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of convertible preferred stock, net of issuance costs (in shares)							141,774	38,970,592
Issuance of convertible preferred stock, net of issuance costs		$ 1,060	$ 319,536				$ 1,060	$ 319,536
Repurchase of common and convertible preferred stock (in shares)				(666,920)					(666,920)	(1,719,308)
Repurchase of common and convertible preferred stock	(7,222)			$ (5,335)					$ (619)			(7,222)				$ (4,716)
Issuance of common stock upon exercise of stock options (in shares)										342,946
Issuance of common stock upon exercise of stock options	753											753
Issuance of common stock upon exercise of warrants (in shares)										89,030
Issuance of common stock upon exercise of warrants	12											12
Vesting of common stock exercised early	103											103
Stock-based compensation	3,670											3,670
Adjustment of redeemable noncontrolling interest	0
Other comprehensive (loss) gain, net of tax impact	(446)													(446)
Net loss	(83,221)														(83,221)
Ending balance (in shares) at Dec. 31, 2017						78,627,369				11,896,882
Ending balance at Dec. 31, 2017	308,606					$ 499,974				$ 0		4,900		(532)	(195,736)
Beginning balance at Dec. 31, 2016					$ 0
Ending balance at Dec. 31, 2017					0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of convertible preferred stock to common stock upon initial public offering (in shares)							(78,627,369)				58,264,577
Conversion of convertible preferred stock to common stock upon initial public offering							$ (499,974)				$ 1		$ 499,973
Issuance of convertible preferred stock, net of issuance costs (in shares)											14,375,000
Issuance of convertible preferred stock, net of issuance costs		$ 249,531											$ 249,531
Repurchase of common and convertible preferred stock (in shares)				(666,920)						(31,681)
Repurchase of common and convertible preferred stock	$ (172)											(172)
Issuance of common stock upon exercise of stock options (in shares)	1,007,387									963,119
Issuance of common stock upon exercise of stock options	$ 2,905											2,905
Issuance of common stock upon early exercise of stock options (in shares)										44,268
Issuance of common stock upon exercise of warrants (in shares)										320,289
Issuance of common stock upon exercise of warrants	45											45
Stock-based compensation	6,851											6,851
Adjustment of redeemable noncontrolling interest	(800)				800										(800)
Other comprehensive (loss) gain, net of tax impact	449													449
Net loss	(84,263)														(84,263)
Ending balance (in shares) at Dec. 31, 2018						0				85,832,454
Ending balance at Dec. 31, 2018	483,152					$ 0				$ 1		764,033		(83)	(280,799)
Increase (Decrease) in Temporary Equity [Roll Forward]
Issuance of equity interests in redeemable noncontrolling interest					41,000
Ending balance at Dec. 31, 2018					41,800
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of convertible preferred stock to common stock upon initial public offering (in shares)										58,264,577
Issuance of common stock upon follow-on offering, net of offering costs (in shares)										5,175,000
Issuance of common stock upon follow-on offering, net of offering costs of $723	$ 349,709											349,709
Issuance of common stock upon exercise of stock options (in shares)	2,999,419									2,999,419
Issuance of common stock upon exercise of stock options	$ 11,638											11,638
Vesting of restricted stock units (in shares)										22,208
Issuance of common stock upon early exercise of stock options (in shares)										0
Issuance of common stock upon early exercise of stock options	95											95
Common stock issued under employee stock purchase plan (in shares)										232,333
Common stock issued under employee stock purchase plan	6,395											6,395
Stock-based compensation	16,954											16,954
Adjustment of redeemable noncontrolling interest	(7,800)				7,800										(7,800)
Other comprehensive (loss) gain, net of tax impact	1,194													1,194
Net loss	(67,851)														(67,851)
Ending balance (in shares) at Dec. 31, 2019						0				94,261,414
Ending balance at Dec. 31, 2019	$ 798,393					$ 0				$ 1		$ 1,150,090		$ 1,111	$ (352,809)
Ending balance at Dec. 31, 2019					$ 49,600