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Stockholders' Equity - Summary of Common Stock Shares Activity (Detail) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Common Stock Outstanding Roll Forward [Roll Forward]    
Beginning balance $ 22,758 $ 12,895
Beginning balance (in shares) 19,663,698  
Net loss $ (4,676) (7,002)
Stock-based compensation expense 398 410
Common stock issued, net of expenses 0 207
Common stock issued through employee stock purchase plan 6 18
Common stock issued for vested restricted stock units (15) (73)
Ending balance $ 25,924 6,455
Ending balance (in shares) 20,625,637  
April 2020 Notes    
Common Stock Outstanding Roll Forward [Roll Forward]    
Common stock issued for conversion of Notes $ 7,453  
Common Stock    
Common Stock Outstanding Roll Forward [Roll Forward]    
Beginning balance $ 20 $ 10
Beginning balance (in shares) 19,663,698 9,741,372
Net loss $ 0 $ 0
Stock-based compensation expense 0 0
Common stock issued, net of expenses $ 0 $ 0
Common stock issued, net of expenses (in shares) 0 28,527
Common stock issued through employee stock purchase plan $ 0 $ 0
Common stock issued through employee stock purchase plan (in shares) 2,184 2,215
Common stock issued for vested restricted stock units $ 0 $ 0
Common stock issued for vested restricted stock units (in shares) 675 15,490
Ending balance $ 21 $ 10
Ending balance (in shares) 20,625,637 9,787,604
Common Stock | April 2020 Notes    
Common Stock Outstanding Roll Forward [Roll Forward]    
Common stock issued for conversion of Notes $ 1  
Common stock issued for conversion of Notes (in shares) 959,080  
Additional Paid-in Capital    
Common Stock Outstanding Roll Forward [Roll Forward]    
Beginning balance $ 349,351 $ 284,313
Net loss 0 0
Stock-based compensation expense 398 410
Common stock issued, net of expenses 0 207
Common stock issued through employee stock purchase plan 6 18
Common stock issued for vested restricted stock units (15) (73)
Ending balance 357,192 284,875
Additional Paid-in Capital | April 2020 Notes    
Common Stock Outstanding Roll Forward [Roll Forward]    
Common stock issued for conversion of Notes 7,452  
Accumulated Deficit    
Common Stock Outstanding Roll Forward [Roll Forward]    
Beginning balance (326,613) (271,428)
Net loss (4,676) (7,002)
Stock-based compensation expense 0 0
Common stock issued, net of expenses 0 0
Common stock issued through employee stock purchase plan 0 0
Common stock issued for vested restricted stock units 0 0
Ending balance (331,289) $ (278,430)
Accumulated Deficit | April 2020 Notes    
Common Stock Outstanding Roll Forward [Roll Forward]    
Common stock issued for conversion of Notes $ 0