Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Current assets:
Allowances for accounts receivables	$ 13	$ 45
Preferred stock, $0.001 par value
Preferred shares (in USD per share)	$ 0.001	$ 0.001
Preferred shares authorized (in shares)	5,000,000	5,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, $0.001 par value
Common stock, par value (in USD per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	100,000,000
Common stock, shares issued (in shares)	34,249,649	31,255,267
Shares outstanding (in shares)	34,249,649	31,255,267