Unaudited Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock A	Common Stock B	Additional Paid-In Capital	Total Accumulated Deficit
Balance, value at Dec. 31, 2019	$ 256,857	$ 28	$ 5	$ 967,317	$ (710,493)
Balance, shares at Dec. 31, 2019		27,878,550	5,318,157
Net loss	(181,976)				(181,976)
Compensation expense related to stock options	45,684			45,684
Exercise of options, value	9,879			9,879
Exercise of options, shares			341,187
Conversion of common stock Class B to Class A, value	1	$ 1
Conversion of common stock Class B to Class A, shares		614,252	(614,252)
Issuance of Common Stock, value	55,399			55,399
Issuance of Common Stock, shares		340,793
Balance, value at Sep. 30, 2020	185,844	$ 29	$ 5	1,078,279	(892,469)
Balance, shares at Sep. 30, 2020		28,833,595	5,045,092
Balance, value at Jun. 30, 2020	231,627	$ 29	$ 5	1,058,606	(827,013)
Balance, shares at Jun. 30, 2020		28,526,532	5,058,319
Net loss	(65,456)				(65,456)
Compensation expense related to stock options	11,580			11,580
Exercise of options, value	8,093			8,093
Exercise of options, shares			293,836
Conversion of common stock Class B to Class A, shares		307,063	(307,063)
Balance, value at Sep. 30, 2020	185,844	$ 29	$ 5	1,078,279	(892,469)
Balance, shares at Sep. 30, 2020		28,833,595	5,045,092
Balance, value at Dec. 31, 2020	417,431	$ 31	$ 5	1,375,640	(958,245)
Balance, shares at Dec. 31, 2020		31,109,154	5,044,931
Net loss	(212,001)				(212,001)
Compensation expense related to stock options	41,580			41,580
Exercise of options, value	$ 8,967			8,967
Exercise of options, shares	229,543		229,543
Issuance of common stock upon vesting of restricted stock units, shares			7,661
Conversion of common stock Class B to Class A, shares		362,886	(362,886)
Balance, value at Sep. 30, 2021	$ 255,977	$ 31	$ 5	1,426,187	(1,170,246)
Balance, shares at Sep. 30, 2021		31,472,040	4,919,249
Balance, value at Jun. 30, 2021	313,829	$ 31	$ 5	1,412,193	(1,098,400)
Balance, shares at Jun. 30, 2021		31,454,329	4,924,479
Net loss	(71,846)				(71,846)
Compensation expense related to stock options	13,657			13,657
Exercise of options, value	337			337
Exercise of options, shares			10,302
Issuance of common stock upon vesting of restricted stock units, shares			2,179
Conversion of common stock Class B to Class A, shares		17,711	(17,711)
Balance, value at Sep. 30, 2021	$ 255,977	$ 31	$ 5	$ 1,426,187	$ (1,170,246)
Balance, shares at Sep. 30, 2021		31,472,040	4,919,249