Consolidated Statements of Stockholders' Deficit - USD ($)
$ in Thousands
Common Stock [Member]
Additional Paid-in Capital [Member]
Retained Earnings [Member]
Total
Balance (in shares) at Dec. 31, 2019 79,573,101      
Balance at Dec. 31, 2019 $ 79 $ 356,609 $ (398,106) $ (41,418)
Stock-based compensation $ 0 4,424 0 4,424
Restricted stock units vested (in shares) 254,684      
Restricted stock units vested $ 0 0 0 0
Tax payments related to shares withheld for restricted stock units vested $ 0 (86) 0 (86)
Net proceeds from issuance of common stock in connection with equity financings (in shares) 18,644,095      
Stock Issued During Period, Value, New Issues $ 19 21,318 0 21,337
Issuance of common stock upon ESPP purchase (in shares) 340,128      
Issuance of common stock upon ESPP purchase $ 0 372 0 372
Net loss $ 0 0 (40,379) (40,379)
Balance (in shares) at Dec. 31, 2020 98,812,008      
Balance at Dec. 31, 2020 $ 98 382,637 (438,485) (55,750) [1]
Stock-based compensation $ 0 4,609 0 4,609
Restricted stock units vested (in shares) 488,715      
Restricted stock units vested $ 0 0 0 0
Tax payments related to shares withheld for restricted stock units vested $ 0 (249) 0 (249)
Net proceeds from issuance of common stock in connection with equity financings (in shares) 37,201,562      
Stock Issued During Period, Value, New Issues $ 38 44,678 0 44,716
Issuance of common stock upon ESPP purchase (in shares) 297,959      
Issuance of common stock upon ESPP purchase $ 0 301 0 301
Net loss 0 0 (35,099) (35,099)
Net proceeds from issuance of warrants in connection with equity financings $ 0 5,562 0 $ 5,562
Issuance of common stock upon exercise of stock options (in shares) 19,403     19,403
Issuance of common stock upon exercise of stock options $ 1 16 0 $ 17
Balance (in shares) at Dec. 31, 2021 136,819,647      
Balance at Dec. 31, 2021 $ 137 $ 437,554 $ (473,584) $ (35,893)
[1] The condensed consolidated balance sheet as of December 31, 2020 has been derived from the audited financial statements as of that date included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2020.