CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Current assets:
Accounts receivable, allowances for doubtful accounts	$ 130	$ 217
Stockholders' equity:
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	2,000,000	2,000,000
Preferred stock, shares issued (in shares)	883,000	883,000
Preferred stock, shares outstanding (in shares)	883,000	883,000
Preferred stock, liquidation preference	$ 7,478	$ 7,346
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	70,000,000	70,000,000
Common stock, shares issued (in shares)	42,657,000	41,967,000
Common stock, shares outstanding (in shares)	42,657,000	41,967,000