Quarterly report pursuant to Section 13 or 15(d)

Warrants - Summary of Warrants Outstanding (Detail)

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Warrants - Summary of Warrants Outstanding (Detail) - $ / shares
6 Months Ended
Jun. 30, 2019
Dec. 31, 2018
Dec. 31, 2017
Class of Warrant or Right [Line Items]      
Warrants Outstanding 26,538,593 7,371,925 2,177,425
Class One [Member]      
Class of Warrant or Right [Line Items]      
Exercise Price $ 3.10    
Warrants Outstanding 48,387    
Expiration Date Sep. 19, 2022    
Class Two [Member]      
Class of Warrant or Right [Line Items]      
Exercise Price $ 2.00    
Warrants Outstanding 900,000    
Expiration Date Apr. 10, 2023    
Class Three [Member]      
Class of Warrant or Right [Line Items]      
Exercise Price $ 3.10    
Warrants Outstanding 462,106    
Expiration Date May 10, 2024    
Class Four [Member]      
Class of Warrant or Right [Line Items]      
Exercise Price $ 3.10    
Warrants Outstanding 602,414    
Expiration Date Jul. 25, 2024    
Class Five [Member]      
Class of Warrant or Right [Line Items]      
Exercise Price $ 3.10    
Warrants Outstanding 1,064,518    
Expiration Date Nov. 08, 2024    
Class Six [Member]      
Class of Warrant or Right [Line Items]      
Exercise Price $ 1.00    
Warrants Outstanding 4,294,500    
Expiration Date Jul. 17, 2025    
Class Seven [Member]      
Class of Warrant or Right [Line Items]      
Exercise Price $ 0.75    
Warrants Outstanding 9,583,334    
Expiration Date Sep. 25, 2020    
Class Eight [Member]      
Class of Warrant or Right [Line Items]      
Exercise Price $ 0.90    
Warrants Outstanding 9,583,334    
Expiration Date Mar. 25, 2024