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Summary of Significant Accounting Policies - Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share for Out of Money Potential Common Shares (Parenthetical) (Detail) - $ / shares
6 Months Ended
Jun. 30, 2019
Jun. 30, 2018
Stock Options With an Exercise Price of $12.48 per Share [Member]    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Stock options exercise price per share $ 12.48 $ 12.48
Stock Options With an Exercise Price of $12.84 per Share [Member]    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Stock options exercise price per share 12.84 12.84
Stock Options With an Exercise Price of $26.40 per Share [Member]    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Stock options exercise price per share 26.40 26.40
Stock Options With an Exercise Price of $39.00 per Share [Member]    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Stock options exercise price per share 39.00 39.00
Stock Options With an Exercise Price of $7.16 per Share [Member]    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Stock options exercise price per share 7.16 7.16
Stock Options With an Exercise Price of $12.00 per Share [Member]    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Stock options exercise price per share $ 12.00 $ 12.00