Quarterly report pursuant to Section 13 or 15(d)

Stockholder's Equity - Summary of Common Stock Shares Activity (Detail)

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Stockholder's Equity - Summary of Common Stock Shares Activity (Detail) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended
Mar. 08, 2018
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Common Stock Outstanding Roll Forward [Roll Forward]          
Beginning balance   $ 26,553 $ 31,656 $ 21,410 $ 34,819
Beginning balance (in shares)       28,971,651  
Cumulative stock-based compensation forfeiture adjustment     1   0
Net loss   351 (8,401) $ (14,410) (17,470)
Stock-based compensation expense   458 407 1,351 1,241
Common stock issued through employee stock purchase plan   21 18 39 36
Common stock issued, net of expenses   498 3,583 19,498 8,638
Common stock issued, net of expenses (in shares) 17,751,500        
Common stock issued for vested restricted stock units   (2)   (9)  
Ending balance   $ 27,879 27,264 $ 27,879 27,264
Ending balance (in shares)   47,193,062   47,193,062  
Common Stock          
Common Stock Outstanding Roll Forward [Roll Forward]          
Beginning balance   $ 47 $ 26 $ 29 $ 24
Beginning balance (in shares)   46,844,072 26,478,051 28,971,651 24,609,411
Cumulative stock-based compensation forfeiture adjustment     $ 0   $ 0
Net loss   $ 0 0 $ 0 0
Stock-based compensation expense   0 0 0 0
Common stock issued through employee stock purchase plan   $ 0 $ 0 $ 0 $ 0
Common stock issued through employee stock purchase plan (in shares)   17,770 10,465 31,361 18,132
Common stock issued, net of expenses   $ 0 $ 2 $ 18 $ 4
Common stock issued, net of expenses (in shares)   328,871 1,847,320 18,181,064 3,708,293
Common stock issued for vested restricted stock units   $ 0   $ 0  
Common stock issued for vested restricted stock units (in shares)   2,349   8,986  
Ending balance   $ 47 $ 28 $ 47 $ 28
Ending balance (in shares)   47,193,062 28,335,836 47,193,062 28,335,836
Additional Paid-in Capital          
Common Stock Outstanding Roll Forward [Roll Forward]          
Beginning balance   $ 246,517 $ 220,890 $ 226,631 $ 214,918
Cumulative stock-based compensation forfeiture adjustment     0   67
Net loss   0 0 0 0
Stock-based compensation expense   458 407 1,351 1,241
Common stock issued through employee stock purchase plan   21 18 39 36
Common stock issued, net of expenses   498 3,581 19,480 8,634
Common stock issued for vested restricted stock units   (2)   (9)  
Ending balance   247,492 224,896 247,492 224,896
Accumulated Deficit          
Common Stock Outstanding Roll Forward [Roll Forward]          
Beginning balance   (220,011) (189,260) (205,250) (180,123)
Cumulative stock-based compensation forfeiture adjustment     1   (67)
Net loss   351 (8,401) (14,410) (17,470)
Stock-based compensation expense   0 0 0 0
Common stock issued through employee stock purchase plan   0 0 0 0
Common stock issued, net of expenses   0 0 0 0
Common stock issued for vested restricted stock units   0   0  
Ending balance   $ (219,660) $ (197,660) $ (219,660) $ (197,660)