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Stock-based Compensation - Summary of RSU Activity (Detail) - RSU [Member]
3 Months Ended
Mar. 31, 2019
$ / shares
shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]  
Unvested-Beginning Balance | shares 11,346
Granted | shares 383,500
Released | shares (416)
Unvested-Ending Balance | shares 394,430
Unvested expected to vest —March 31, 2019 | shares 394,430
Unvested-Beginning Balance | $ / shares $ 3.60
Granted | $ / shares 1.76
Released | $ / shares 3.04
Unvested-Ending Balance | $ / shares 1.81
Unvested expected to vest —March 31, 2019 | $ / shares $ 1.81