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Stockholders' Equity - Stock Options, Activity (Detail)
6 Months Ended
Jun. 30, 2021
$ / shares
shares
Number of Option Shares  
Outstanding, Beginning | shares 2,171,477
Granted | shares 1,363,875
Forfeited | shares (331,824)
Expired | shares (1,151)
Outstanding, Ending | shares 3,202,377
Options exercisable | shares 1,393,630
Options unvested | shares 1,808,747
Weighted Average Exercise Price  
Outstanding, Beginning | $ / shares $ 5.62
Granted | $ / shares 3.02
Forfeited | $ / shares 4.57
Expired | $ / shares 10.00
Outstanding, Ending | $ / shares 4.62
Options exercisable | $ / shares 5.12
Options unvested | $ / shares $ 4.24