Condensed Unaudited Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity / (Deficit) - USD ($) $ in Thousands	Total	Treasury Stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Loss	Redeemable Convertible Preferred Stock	Series A Common Stock [Member]	Series B common stock [Member]	Class A Common Stock [Member]	Class B Common Stock [Member]
Balance at Dec. 31, 2019	$ (186,334)	$ (23,469)	$ 27,909	$ (189,029)	$ (1,847)	$ 154,210	$ 99	$ 3
Balance (in shares) at Dec. 31, 2019		(8,195,464)				39,223,194	99,339,942	3,054,318
Restricted stock grants			(4)				$ 4
Restricted stock grants (in shares)							3,975,634
Restricted stock forfeitures			1				$ (1)
Restricted stock forfeitures (in shares)							(997,094)
Foreign currency translation adjustment	(741)				(741)
Net loss	(16,380)			(16,380)
Stock-based compensation	26		26
Shares issued in connection with an agreement	423		423
Shares issued in connection with an agreement (in shares)							154,560
Balance (in shares) at Mar. 31, 2020		(8,195,464)				39,223,194	102,473,042	3,054,318
Balance at Mar. 31, 2020	(203,006)	$ (23,469)	28,355	(205,409)	(2,588)	$ 154,210	$ 102	$ 3
Balance at Dec. 31, 2019	(186,334)	$ (23,469)	27,909	(189,029)	(1,847)	$ 154,210	$ 99	$ 3
Balance (in shares) at Dec. 31, 2019		(8,195,464)				39,223,194	99,339,942	3,054,318
Foreign currency translation adjustment	(516)
Net loss	(44,437)
Balance (in shares) at Sep. 30, 2020		(8,195,464)				39,223,194	111,500,433	3,054,318
Balance at Sep. 30, 2020	(230,785)	$ (23,469)	28,398	(233,466)	(2,363)	$ 154,210	$ 112	$ 3
Balance at Mar. 31, 2020	(203,006)	$ (23,469)	28,355	(205,409)	(2,588)	$ 154,210	$ 102	$ 3
Balance (in shares) at Mar. 31, 2020		(8,195,464)				39,223,194	102,473,042	3,054,318
Restricted stock grants			(1)				$ 1
Restricted stock grants (in shares)							1,148,962
Restricted stock forfeitures (in shares)							(383,695)
Foreign currency translation adjustment	(47)				(47)
Net loss	(15,054)			(15,054)
Stock-based compensation	27		27
Balance (in shares) at Jun. 30, 2020		(8,195,464)				39,223,194	103,238,309	3,054,318
Balance at Jun. 30, 2020	(218,080)	$ (23,469)	28,381	(220,463)	(2,635)	$ 154,210	$ 103	$ 3
Restricted stock grants			(9)				$ 9
Restricted stock grants (in shares)							8,743,780
Restricted stock forfeitures (in shares)							(481,656)
Foreign currency translation adjustment	272				272
Net loss	(13,003)			(13,003)
Stock-based compensation	26		26
Balance (in shares) at Sep. 30, 2020		(8,195,464)				39,223,194	111,500,433	3,054,318
Balance at Sep. 30, 2020	(230,785)	$ (23,469)	28,398	(233,466)	(2,363)	$ 154,210	$ 112	$ 3
Balance at Dec. 31, 2020	(239,220)	$ (23,469)	28,425	(242,254)	(2,037)	$ 154,210	$ 112	$ 3
Balance (in shares) at Dec. 31, 2020		(8,195,464)				39,223,194	112,012,693	3,054,318
Shares issued in connection with an acquisition	5,454		5,453				$ 1
Shares issued in connection with an acquisition (in shares)							613,497
Restricted stock grants			(4)				$ 4
Restricted stock grants (in shares)							3,687,431
Restricted stock forfeitures			2				$ (2)
Restricted stock forfeitures (in shares)							(1,629,369)
Restricted stock cancelation			18				$ (18)
Restricted stock cancelation (in shares)							(17,853,416)
Foreign currency translation adjustment	54				54
Net loss	(24,374)			(24,374)
Balance (in shares) at Mar. 31, 2021		(8,195,464)				39,223,194	96,830,836	3,054,318
Balance at Mar. 31, 2021	(258,086)	$ (23,469)	33,894	(266,628)	(1,983)	$ 154,210	$ 97	$ 3
Balance at Dec. 31, 2020	(239,220)	$ (23,469)	28,425	(242,254)	(2,037)	$ 154,210	$ 112	$ 3
Balance (in shares) at Dec. 31, 2020		(8,195,464)				39,223,194	112,012,693	3,054,318
Foreign currency translation adjustment	(152)
Net loss	(188,425)
Shares repurchased (in shares)										(2,307,692)
Balance (in shares) at Sep. 30, 2021		(8,195,464)							155,022,167	37,856,095
Balance at Sep. 30, 2021	55,785	$ (23,469)	511,929	(430,679)	(2,189)				$ 155	$ 38
Balance at Mar. 31, 2021	(258,086)	$ (23,469)	33,894	(266,628)	(1,983)	$ 154,210	$ 97	$ 3
Balance (in shares) at Mar. 31, 2021		(8,195,464)				39,223,194	96,830,836	3,054,318
Restricted stock grants			(2)						$ 1	$ 1
Restricted stock grants (in shares)									1,155,598	700,000
Restricted stock forfeitures			2						$ (2)
Restricted stock forfeitures (in shares)									(2,334,753)
Foreign currency translation adjustment	(129)				(129)
Net loss	(94,922)			(94,922)
Conversion of Series A and Series B common shares into Class A and Class B common shares, respectively			1				$ (97)	$ (3)	$ 60	$ 39
Conversion of Series A and Series B common shares into Class A and Class B common shares, respectively (in shares)							(96,830,836)	(3,054,318)	60,421,367	39,463,787
Warrants exercised	24,140		24,132						$ 8
Warrants exercised (in shares)									8,360,331
Conversion of redeemable convertible preferred stock to Class A Common Stock	193,210		193,136			$ (154,210)			$ 74
Conversion of redeemable convertible preferred stock to Class A Common Stock (in shares)						(39,223,194)			73,813,713
Shares issued in connection with the Initial Public Offering	147,739		147,724						$ 15
Shares issued in connection with the Initial Public Offering (in shares)									14,773,939
Equity issuance cost	(21,201)		(21,201)
Shares repurchased	(64,468)		(64,462)						$ (4)	$ (2)
Shares repurchased (in shares)									(4,138,866)	(2,307,692)
Restricted stock units vesting (in shares)									219,072
Stock-based compensation	126,775		126,775
Balance (in shares) at Jun. 30, 2021		(8,195,464)							152,270,401	37,856,095
Balance at Jun. 30, 2021	53,058	$ (23,469)	439,999	(361,550)	(2,112)				$ 152	$ 38
Restricted stock grants			(3)						$ 3	$ 0
Restricted stock grants (in shares)									3,281,016	0
Restricted stock forfeitures			0						$ 0
Restricted stock forfeitures (in shares)									(718,056)
Foreign currency translation adjustment	(77)				(77)
Net loss	(69,129)			(69,129)
Shares repurchased	0		0						$ 0	$ 0
Shares repurchased (in shares)									(37,679)	0
Stock-based compensation	70,668		70,668
Shares issued in connection with settlement of a dispute	1,196		1,196
Shares issued in connection with settlement of a dispute (in shares)									200,000
Options exercised	69		69
Options exercised (in shares)									26,485
Balance (in shares) at Sep. 30, 2021		(8,195,464)							155,022,167	37,856,095
Balance at Sep. 30, 2021	$ 55,785	$ (23,469)	$ 511,929	$ (430,679)	$ (2,189)				$ 155	$ 38