Quarterly report pursuant to Section 13 or 15(d)

Stock Warrants - Schedule of Warrants Outstanding (Detail)

v3.19.1
Stock Warrants - Schedule of Warrants Outstanding (Detail) - $ / shares
3 Months Ended
Mar. 31, 2019
Dec. 31, 2018
Aug. 01, 2014
Class of Warrant or Right [Line Items]      
Shares Underlying Outstanding Warrants 30,987,114 31,243,026  
Weighted-average exercise price per share $ 2.31 $ 2.31  
Placement Agent Warrants [Member]      
Class of Warrant or Right [Line Items]      
Shares Underlying Outstanding Warrants 189,126 189,126  
Representative's Warrant [Member]      
Class of Warrant or Right [Line Items]      
Shares Underlying Outstanding Warrants 206,410 206,410  
Exercise Prices $ 7.50    
Other Warrants [Member]      
Class of Warrant or Right [Line Items]      
Shares Underlying Outstanding Warrants [1] 180,338 180,338  
Exercise Price Less Than or Equal to $2.00 [Member]      
Class of Warrant or Right [Line Items]      
Shares Underlying Outstanding Warrants 16,002,164    
Expiration Start Date Sep. 01, 2021    
Expiration End Date Jul. 25, 2022    
Exercise Price $2.01 - $4.99 [Member]      
Class of Warrant or Right [Line Items]      
Shares Underlying Outstanding Warrants 14,705,017    
Expiration Start Date Jun. 12, 2019    
Expiration End Date Jul. 27, 2021    
Exercise Price Greater Than or Equal to $ 5.00 [Member]      
Class of Warrant or Right [Line Items]      
Shares Underlying Outstanding Warrants 279,933    
Expiration Start Date Jul. 22, 2019    
Expiration End Date Jan. 05, 2022    
Minimum [Member] | Exercise Price $2.01 - $4.99 [Member]      
Class of Warrant or Right [Line Items]      
Exercise Prices $ 2.01    
Minimum [Member] | Exercise Price Greater Than or Equal to $ 5.00 [Member]      
Class of Warrant or Right [Line Items]      
Exercise Prices 5.00    
Maximum [Member] | Exercise Price Less Than or Equal to $2.00 [Member]      
Class of Warrant or Right [Line Items]      
Exercise Prices 2.00    
Maximum [Member] | Exercise Price $2.01 - $4.99 [Member]      
Class of Warrant or Right [Line Items]      
Exercise Prices $ 4.99    
Note Warrants [Member]      
Class of Warrant or Right [Line Items]      
Shares Underlying Outstanding Warrants 414,790 670,702 3,321,416
Exercise Prices     $ 3.00
2016 Warrants [Member]      
Class of Warrant or Right [Line Items]      
Shares Underlying Outstanding Warrants 14,000,000 14,000,000  
2017 Warrants [Member]      
Class of Warrant or Right [Line Items]      
Shares Underlying Outstanding Warrants 15,996,450 15,996,450  
[1] Other warrants are comprised of warrants issued prior to the Company’s IPO, generally in exchange for services rendered to the Company.