Quarterly report pursuant to Section 13 or 15(d)

Summary of Significant Accounting Policies - Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share (Detail)

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Summary of Significant Accounting Policies - Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share (Detail) - shares
 3 Months Ended 9 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Summary Of Significant Accounting Policies [Line Items]        
Potentially dilutive securities 6,840,737 7,862,420 6,840,737 7,862,420
Financing Warrant to Purchase Common Stock [Member]        
Summary Of Significant Accounting Policies [Line Items]        
Potentially dilutive securities   13,889   13,889
IPO Warrants to Purchase Common Stock [Member]        
Summary Of Significant Accounting Policies [Line Items]        
Potentially dilutive securities   11,600   11,600
Warrant Issued to Private Investors [Member]        
Summary Of Significant Accounting Policies [Line Items]        
Potentially dilutive securities 3,035,688 3,035,688 3,035,688 3,035,688
Employee Stock Option [Member]        
Summary Of Significant Accounting Policies [Line Items]        
Potentially dilutive securities 656,494 1,149,589 656,494 1,149,589
Restricted Stock Units (RSUs) [Member]        
Summary Of Significant Accounting Policies [Line Items]        
Potentially dilutive securities 2,276,996 2,498,037 2,276,996 2,498,037
Performance Share Units [Member]        
Summary Of Significant Accounting Policies [Line Items]        
Potentially dilutive securities 871,559 1,153,617 871,559 1,153,617