Quarterly report pursuant to Section 13 or 15(d)

Summary of Significant Accounting Policies - Anti-Dilutive Securities Excluded from the Computation of Diluted Net Loss per Share (Detail)

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Summary of Significant Accounting Policies - Anti-Dilutive Securities Excluded from the Computation of Diluted Net Loss per Share (Detail) - shares
shares in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Anti-dilutive securities excluded from the computation of diluted loss per share 6,138 6,036 6,138 6,036
Common Stock Warrants [Member]        
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Anti-dilutive securities excluded from the computation of diluted loss per share 729 1,667 729 1,667
Common Stock Options [Member]        
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Anti-dilutive securities excluded from the computation of diluted loss per share 5,074 3,803 5,074 3,803
Performance Based Stock Option [Member]        
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Anti-dilutive securities excluded from the computation of diluted loss per share 205 327 205 327
Incentive Awards [Member]        
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Anti-dilutive securities excluded from the computation of diluted loss per share 130 239 130 239