Annual report pursuant to Section 13 and 15(d)

Capitalization and Equity Structure - 2014 PPO and Merger Warrants and Pre-Merger Warrants (Details)

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Capitalization and Equity Structure - 2014 PPO and Merger Warrants and Pre-Merger Warrants (Details) - $ / shares
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Apr. 30, 2017
Dec. 31, 2015
Jan. 15, 2014
Class of Warrant or Right [Line Items]            
Number warrants called (in shares)         2,122,000 89,000
Merger/PPO Warrant Shares Exercised (in shares) 0          
2015 Warrants            
Class of Warrant or Right [Line Items]            
Exercise price (in dollars per share) $ 3.74          
Merger/PPO Warrant Shares Exercised (in shares) 0 30,000 488,000      
Warrants for common stock            
Class of Warrant or Right [Line Items]            
Number warrants called (in shares)           5,151,000
Exercise price (in dollars per share)           $ 7.00
Warrants for common stock | Merger and PPO            
Class of Warrant or Right [Line Items]            
Number warrants called (in shares)           4,329,000
Exercise price (in dollars per share)           $ 14.00
Common Stock            
Class of Warrant or Right [Line Items]            
Number warrants called (in shares) 88,000     1,866,000    
Exercise price (in dollars per share) $ 9.66