Condensed Consolidated Statements of Changes in Stockholders' Deficit (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Deficit
Balance (in shares) at Dec. 31, 2019		33,562,885
Balance at Dec. 31, 2019	$ (6,122)	$ 34	$ 124,318	$ (130,474)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation expense	1,860		1,860
Vested restricted stock units (in shares)		19,811
Vested restricted stock units	(37)		(37)
Net loss	(16,530)			(16,530)
Balance (in shares) at Mar. 31, 2020		33,582,696
Balance at Mar. 31, 2020	(20,829)	$ 34	126,141	(147,004)
Balance (in shares) at Dec. 31, 2019		33,562,885
Balance at Dec. 31, 2019	$ (6,122)	$ 34	124,318	(130,474)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under employee stock purchase plan (in shares)	14,961
Net loss	$ (35,415)
Balance (in shares) at Sep. 30, 2020		33,619,796
Balance at Sep. 30, 2020	(36,519)	$ 34	129,336	(165,889)
Balance (in shares) at Mar. 31, 2020		33,582,696
Balance at Mar. 31, 2020	(20,829)	$ 34	126,141	(147,004)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under employee stock purchase plan (in shares)		14,961
Shares issued under employee stock purchase plan	73		73
Share-based compensation expense	1,754		1,754
Vested restricted stock units (in shares)		18,944
Vested restricted stock units	(52)		(52)
Net loss	(2,334)			(2,334)
Balance (in shares) at Jun. 30, 2020		33,616,601
Balance at Jun. 30, 2020	(21,388)	$ 34	127,916	(149,338)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation expense (in shares)		3,195
Share-based compensation expense	1,420		1,420
Net loss	(16,551)			(16,551)
Balance (in shares) at Sep. 30, 2020		33,619,796
Balance at Sep. 30, 2020	(36,519)	$ 34	129,336	(165,889)
Balance (in shares) at Dec. 31, 2020		34,569,254
Balance at Dec. 31, 2020	(48,497)	$ 35	137,725	(186,257)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock issued under public equity offering (in shares)		1,672,104
Common Stock issued under public equity offering	10,197	$ 1	10,196
Costs of common stock issued under public equity offering	(306)		(306)
Share-based compensation expense	1,507		1,507
Other	(27)		(27)
Net loss	(14,672)			(14,672)
Balance (in shares) at Mar. 31, 2021		36,241,358
Balance at Mar. 31, 2021	(51,798)	$ 36	149,095	(200,929)
Balance (in shares) at Dec. 31, 2020		34,569,254
Balance at Dec. 31, 2020	$ (48,497)	$ 35	137,725	(186,257)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under employee stock purchase plan (in shares)	19,270
Net loss	$ (41,594)
Balance (in shares) at Sep. 30, 2021		40,083,245
Balance at Sep. 30, 2021	(60,345)	$ 40	167,466	(227,851)
Balance (in shares) at Mar. 31, 2021		36,241,358
Balance at Mar. 31, 2021	(51,798)	$ 36	149,095	(200,929)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock issued under public equity offering (in shares)		2,304,949
Common Stock issued under public equity offering	9,241	$ 3	9,238
Costs of common stock issued under public equity offering	(627)		(627)
Shares issued under employee stock purchase plan (in shares)		19,270
Shares issued under employee stock purchase plan	76		76
Share-based compensation expense	1,710		1,710
Vested restricted stock units (in shares)		2,665
Vested restricted stock units	(4)		(4)
Net loss	(12,367)			(12,367)
Balance (in shares) at Jun. 30, 2021		38,568,242
Balance at Jun. 30, 2021	(53,769)	$ 39	159,488	(213,296)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock issued under public equity offering (in shares)		1,509,818
Common Stock issued under public equity offering	6,222	$ 1	6,221
Costs of common stock issued under public equity offering	(135)		(135)
Share-based compensation expense	1,900		1,900
Vested restricted stock units (in shares)		5,185
Vested restricted stock units	(9)		(9)
Other	1		1
Net loss	(14,555)			(14,555)
Balance (in shares) at Sep. 30, 2021		40,083,245
Balance at Sep. 30, 2021	$ (60,345)	$ 40	$ 167,466	$ (227,851)