Annual report pursuant to Section 13 and 15(d)

Fair Value Measurements - Avenue's Contingently Issuable Warrants with option pricing model (Detail)

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Fair Value Measurements - Avenue's Contingently Issuable Warrants with option pricing model (Detail)
1 Months Ended 5 Months Ended 12 Months Ended
Oct. 30, 2015
Aug. 31, 2015
Dec. 31, 2017
Dec. 31, 2016
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]        
Expected dividend yield     0.00%  
Expected volatility     70.00%  
Avenue [Member]        
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]        
Risk-free interest rate     0.00% 2.45%
Expected dividend yield     0.00% 0.00%
Expected term in years     0 years 10 years
Expected volatility     0.00% 87.00%
Probability of issuance of the warrant     0.00% 50.00%
Mustang [Member] | Contingently Issuable Warrants [Member]        
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]        
Risk-free interest rate     1.37%  
Expected dividend yield     0.00%  
Expected term in years     10 years  
Expected volatility     76.70%  
Probability of issuance of the warrant     100.00%  
Checkpoint [Member] | Contingently Issuable Warrants [Member]        
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]        
Risk-free interest rate 2.16% 2.26%    
Expected dividend yield 0.00% 0.00%    
Expected term in years 10 years 10 years    
Expected volatility 100.86% 83.00%    
Probability of issuance of the warrant 100.00% 25.00%