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Warrants - Calculated Aggregated Fair Values and Assumptions (Details) - Warrant Liability - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Class of Warrant or Right [Line Items]    
Calculated aggregate value $ 6,034 $ 8,275
Weighted average exercise price per share of warrant (usd per share) $ 1.99 $ 7.14
Closing price per share of common stock (usd per share) $ 0.63 $ 4.55
Volatility 85.60% 85.20%
Contractual remaining term 4 years 3 months 1 year 8 months
Risk-free interest rate 1.75% 0.98%
Dividend yield 0.00% 0.00%