Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In-Capital	Accumulated Deficit
Beginning balance at Dec. 31, 2019	$ 11,157	$ 44	$ 248,770	$ (237,657)
Beginning balance, shares at Dec. 31, 2019		44,413,372
Issuance of common shares under at-the-market sales agreement	1,193	$ 1	1,192
Issuance of common shares under at-the-market sales agreement, shares		455,186
Share-based compensation expense	1,001		1,001
Net loss	(2,911)			(2,911)
Ending balance at Mar. 31, 2020	10,440	$ 45	250,963	(240,568)
Ending balance, shares at Mar. 31, 2020		44,868,558
Beginning balance at Dec. 31, 2020	8,763	$ 52	264,578	(255,867)
Beginning balance, shares at Dec. 31, 2020		51,860,941
Issuance of common shares under a direct registered offering	11,078	$ 4	11,074
Issuance of common shares under a direct registered offering, shares		4,209,050
Issuance of common shares under at-the-market sales agreement	3,249	$ 2	3,247
Issuance of common shares under at-the-market sales agreement, shares		1,186,579
Vesting of restricted stock units, shares		227,754
Exercise of stock options	38		38
Exercise of stock options, shares		62,493
Issuance of common shares under employee stock purchase plan	54		54
Issuance of common shares under employee stock purchase plan, shares		31,908
Share-based compensation expense	1,154		1,154
Net loss	(7,351)			(7,351)
Ending balance at Mar. 31, 2021	$ 16,985	$ 58	$ 280,145	$ (263,218)
Ending balance, shares at Mar. 31, 2021		57,578,725