CONDENSED CONSOLIDATED STATEMENTS OF CONVERTIBLE PREFERRED STOCK, REDEEMABLE COMMON STOCK AND STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) $ in Thousands	Total	Redeemable Common Stock	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit
Beginning balance, shares at Dec. 31, 2019			16,128,862
Beginning balance at Dec. 31, 2019	$ 129,220		$ 16	$ 261,367	$ (119)	$ (132,044)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options, shares			13,006
Exercise of stock options	96			96
Stock-based compensation expense	613			613
Net loss	(11,138)					(11,138)
Ending balance, shares at Mar. 31, 2020			16,141,868
Ending balance at Mar. 31, 2020	118,791		$ 16	262,076	(119)	(143,182)
Beginning balance, shares at Dec. 31, 2019			16,128,862
Beginning balance at Dec. 31, 2019	129,220		$ 16	261,367	(119)	(132,044)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	$ (43,731)
Ending balance, shares at Sep. 30, 2020	16,286,645
Ending balance at Sep. 30, 2020	$ 89,708		$ 16	265,586	(119)	(175,775)
Beginning balance, shares at Mar. 31, 2020			16,141,868
Beginning balance at Mar. 31, 2020	118,791		$ 16	262,076	(119)	(143,182)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares under employee stock purchase plan, shares			10,057
Issuance of shares under employee stock purchase plan	76			76
Vesting of restricted stock units, less shares withheld and retired to satisfy tax obligations, shares			23,822
Exercise of stock options, shares			407
Exercise of stock options	2			2
Vesting of restricted stock units, less shares withheld and retired to satisfy tax obligations	(14)		$ (14)
Stock-based compensation expense	1,173			1,173
Net loss	$ (15,144)					(15,144)
Ending balance, shares at Jun. 30, 2020	16,176,154
Ending balance at Jun. 30, 2020	$ 104,884		$ 16	263,313	(119)	(158,326)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Vesting of restricted stock units, less shares withheld and retired to satisfy tax obligations, shares			106,215
Exercise of stock options, shares			4,276
Exercise of stock options	29			29
Vesting of restricted stock units, less shares withheld and retired to satisfy tax obligations	0
Stock-based compensation expense	2,244			2,244
Net loss	$ (17,449)					(17,449)
Ending balance, shares at Sep. 30, 2020	16,286,645
Ending balance at Sep. 30, 2020	$ 89,708		$ 16	265,586	(119)	(175,775)
Increase (Decrease) in Temporary Equity [Roll Forward]
Redeemable Common Shares, Value		$ 0
Redeemable common shares, beginning balance, shares at Dec. 31, 2020		0
Convertible preferred shares, ending balance, shares at Mar. 31, 2021		229,885
Beginning balance, shares at Dec. 31, 2020			16,305,731
Beginning balance at Dec. 31, 2020	72,799		$ 16	267,077	(119)	(194,175)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock Issued During Period, Shares, New Issues		229,885	6,041,951
Stock Issued During Period, Value, New Issues	49,640	$ 1,875	$ 7	49,633
Stock Issued During Period Shares Warrants Exercised			1,072,887
Stock Issued During Period Value Warrants Exercised	1		$ 1
Exercise of stock options, shares			5,860
Exercise of stock options	40			40
Stock-based compensation expense	1,258			1,258
Net loss	(18,676)					(18,676)
Ending balance, shares at Mar. 31, 2021			23,426,429
Ending balance at Mar. 31, 2021	105,062		$ 24	318,008	(119)	(212,851)
Redeemable common shares, beginning balance, shares at Dec. 31, 2020		0
Convertible preferred shares, ending balance, shares at Sep. 30, 2021		0
Beginning balance, shares at Dec. 31, 2020			16,305,731
Beginning balance at Dec. 31, 2020	$ 72,799		$ 16	267,077	(119)	(194,175)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options, shares	5,860
Net loss	$ (58,489)
Ending balance, shares at Sep. 30, 2021			24,708,727
Ending balance at Sep. 30, 2021	68,679		$ 25	321,437	(119)	(252,664)
Increase (Decrease) in Temporary Equity [Roll Forward]
Redeemable Common Shares, Value		$ 1,875
Redeemable common shares, beginning balance, shares at Mar. 31, 2021		229,885
Convertible preferred shares, ending balance, shares at Jun. 30, 2021		229,885
Beginning balance, shares at Mar. 31, 2021			23,426,429
Beginning balance at Mar. 31, 2021	105,062		$ 24	318,008	(119)	(212,851)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares under employee stock purchase plan, shares			20,232
Issuance of shares under employee stock purchase plan	116			116
Stock Issued During Period Shares Warrants Exercised			1,056,881
Stock Issued During Period Value Warrants Exercised	1		$ 1
Vesting of restricted stock units, less shares withheld and retired to satisfy tax obligations, shares			81,316
Vesting of restricted stock units, less shares withheld and retired to satisfy tax obligations	0
Stock-based compensation expense	1,797			1,797
Net loss	(19,638)
Ending balance, shares at Jun. 30, 2021			24,584,858
Ending balance at Jun. 30, 2021	$ 87,338		$ 25	319,921	(119)	(232,489)
Increase (Decrease) in Temporary Equity [Roll Forward]
Redeemable Common Shares, Value		$ 1,875
Convertible preferred shares, ending balance, shares at Sep. 30, 2021		0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock Issued During Period, Shares, New Issues	6,271,836
Vesting of restricted stock units, less shares withheld and retired to satisfy tax obligations, shares			123,869
Vesting of restricted stock units, less shares withheld and retired to satisfy tax obligations	$ 0
Stock-based compensation expense	$ 1,516			1,516
Repurchase and retirement of redeemable common stock	229,885
Repurchase and retirement of redeemable common stock	$ 0	$ 1,875
Net loss	(20,175)
Ending balance, shares at Sep. 30, 2021			24,708,727
Ending balance at Sep. 30, 2021	$ 68,679		$ 25	$ 321,437	$ (119)	$ (252,664)
Increase (Decrease) in Temporary Equity [Roll Forward]
Redeemable Common Shares, Value		$ 0