Quarterly report pursuant to Section 13 or 15(d)

Warrants - Summary of Warrant Activity (Details)

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Warrants - Summary of Warrant Activity (Details)
shares in Thousands
 3 Months Ended
Mar. 31, 2018
$ / shares
shares
Class of Warrant or Right [Line Items]  
Warrants Exercise Price (usd per share) | $ / shares $ 3.8
Warrants Outstanding (in shares) | shares 10,055
Warrant Issued With | Non-derivative warrants  
Class of Warrant or Right [Line Items]  
Warrants Exercise Price (usd per share) | $ / shares $ 6
Warrants Outstanding (in shares) | shares 3,969
Warrant Issued For | Derivative warrants  
Class of Warrant or Right [Line Items]  
Warrants Exercise Price (usd per share) | $ / shares $ 2.36
Warrants Outstanding (in shares) | shares 6,086
Financing | Warrant Issued With | Non-derivative warrants  
Class of Warrant or Right [Line Items]  
Warrants Exercise Price (usd per share) | $ / shares $ 10.00
Warrants Outstanding (in shares) | shares 243
Financing | Warrant Issued With | Non-derivative warrants  
Class of Warrant or Right [Line Items]  
Warrants Exercise Price (usd per share) | $ / shares $ 15.00
Warrants Outstanding (in shares) | shares 276
2017 Debt | Warrant Issued For | Derivative warrants  
Class of Warrant or Right [Line Items]  
Warrants Exercise Price (usd per share) | $ / shares $ 2.82
Warrants Outstanding (in shares) | shares 443
2015 Offering | Warrant Issued With | Non-derivative warrants  
Class of Warrant or Right [Line Items]  
Warrants Exercise Price (usd per share) | $ / shares $ 5
Warrants Outstanding (in shares) | shares 3,450
2016 Offerings | Warrant Issued For | Derivative warrants  
Class of Warrant or Right [Line Items]  
Warrants Exercise Price (usd per share) | $ / shares $ 2.25
Warrants Outstanding (in shares) | shares 1,968
2017 Offering | Warrant Issued For | Derivative warrants  
Class of Warrant or Right [Line Items]  
Warrants Exercise Price (usd per share) | $ / shares $ 2.35
Warrants Outstanding (in shares) | shares 3,500
2017 Offering | Warrant Issued For | Derivative warrants  
Class of Warrant or Right [Line Items]  
Warrants Exercise Price (usd per share) | $ / shares $ 2.5
Warrants Outstanding (in shares) | shares 175