Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Loss [Member]
Balances at beginning of period at Dec. 31, 2019	$ 21,060	$ 7	$ 299,263	$ (277,112)	$ (1,098)
Balances at beginning of period (in shares) at Dec. 31, 2019		6,810,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net proceeds from common stock sold	$ 7,500	$ 3	7,497
Common stock sold under agreement | shares	2,726,000	2,726,000
Issuance of common stock from vesting of restricted stock units (in shares)		186,000
Tax withholding related to vesting of restricted stock units	$ (215)		(215)
Issuance of common stock under employee stock purchase plan	26		26
Issuance of common stock under employee stock purchase plan (in shares)		21,000
Stock-based compensation expense	1,494		1,494
Net loss	(14,051)			(14,051)
Foreign currency translation adjustments	1				1
Balances at end of period at Dec. 31, 2020	15,815	$ 10	308,065	(291,163)	(1,097)
Balances at end of period (in shares) at Dec. 31, 2020		9,743,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net proceeds from common stock sold	41,642	$ 5	41,637
Common stock sold under agreement | shares		5,502,000
Issuance of common stock from vesting of restricted stock units (in shares)		264,000
Tax withholding related to vesting of restricted stock units	(444)		(444)
Issuance of common stock under employee stock purchase plan	28		28
Issuance of common stock under employee stock purchase plan (in shares)		23,000
Stock-based compensation expense	2,108		2,108
Net loss	(12,944)			(12,944)
Foreign currency translation adjustments	53				53
Balances at end of period at Dec. 31, 2021	$ 46,258	$ 15	$ 351,394	$ (304,107)	$ (1,044)
Balances at end of period (in shares) at Dec. 31, 2021		15,532,000