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	(48,939)				(48,939)
Compensation expense related to stock options	19,307			19,307
Exercise of options, value	1,422			1,422
Exercise of options, shares			40,216
Conversion of common stock Class B to Class A, shares		288,102	(288,102)
Balance, value at Mar. 31, 2020	228,647	$ 28	$ 5	988,046	(759,432)
Balance, shares at Mar. 31, 2020		28,166,652	5,070,271
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	(67,455)				(67,455)
Compensation expense related to stock options	14,679			14,679
Exercise of options, value	$ 4,678			4,678
Exercise of options, shares	112,423		112,423
Issuance of common stock upon vesting of restricted stock units, shares			3,302
Conversion of common stock Class B to Class A, shares		251,102	(251,102)
Balance, value at Mar. 31, 2021	$ 369,333	$ 31	$ 5	$ 1,394,997	$ (1,025,700)
Balance, shares at Mar. 31, 2021		31,360,256	4,909,554