Quarterly report pursuant to Section 13 or 15(d)

Warrant Liability - Assumptions Used and Summary of Warrant Liability (Details)

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Warrant Liability - Assumptions Used and Summary of Warrant Liability (Details) - $ / shares
6 Months Ended 12 Months Ended
Jun. 30, 2018
Dec. 31, 2017
Minimum | Warrant    
Number of Shares Under Warrant    
Range of warrant price per share, granted (in dollars per share)   $ 1.35
Maximum | Warrant    
Number of Shares Under Warrant    
Range of warrant price per share, granted (in dollars per share)   $ 1.50
June 2018 Warrants    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Volatility rate 80.00%  
Dividend yield 0.00%  
Number of Shares Under Warrant    
Number of shares under warrant, balance at beginning of period 0  
Number of shares under warrant, granted 742,991  
Number of shares under warrant, exercised 0  
Number of shares under warrant, expired 0  
Number of shares under warrant, balance at end of period 742,991 0
Number of shares under warrant, vested and exercisable at period end 0  
Weighted Average Exercise Price    
Weighted average exercise price, outstanding, period start (in dollars per share) $ 0  
Weighted average exercise price, granted (in dollars per share) 2.03  
Weighted average exercise price, exercised (in dollars per share) 0  
Weighted average exercise price, expired (in dollars per share) 0  
Weighted average exercise price, outstanding, period end (in dollars per share) 2.03  
Weighted average exercise price, vested and exercisable, period end (in dollars per share) $ 2.03  
Weighted Average Remaining Contractual Life (Years)    
Weighted average remaining contractual life, balance (in years) 5 years 5 months 19 days 0 years
Weighted average remaining contractual life, granted (in years) 5 years 5 months 19 days  
Weighted average remaining contractual life, exercised (in years) 0 years  
Weighted average remaining contractual life, expired (in years) 0 years  
Weighted average remaining contractual life, vested and exercisable at period end (in years) 0 years  
June 2018 Warrants | Minimum    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Risk-free interest rate 2.73%  
Expected life (years) 4 years 11 months 19 days  
Number of Shares Under Warrant    
Range of warrant price per share, granted (in dollars per share) $ 2.02  
Range of warrant price per share, outstanding, end of period (in dollars per share) 2.02  
Range of warrant price per share, vested and exercisable at period end (in dollars per share) $ 2.02  
June 2018 Warrants | Maximum    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Risk-free interest rate 2.80%  
Expected life (years) 5 years 5 months 23 days  
Number of Shares Under Warrant    
Range of warrant price per share, granted (in dollars per share) $ 2.32  
Range of warrant price per share, outstanding, end of period (in dollars per share) 2.32  
Range of warrant price per share, vested and exercisable at period end (in dollars per share) $ 2.32  
February 2018 Warrants    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Volatility rate 80.00%  
Dividend yield 0.00%  
Number of Shares Under Warrant    
Number of shares under warrant, balance at beginning of period 0  
Number of shares under warrant, granted 2,273,700  
Number of shares under warrant, exercised 0  
Number of shares under warrant, expired 0  
Number of shares under warrant, balance at end of period 2,273,700 0
Number of shares under warrant, vested and exercisable at period end 0  
Range of warrant price per share, granted (in dollars per share) $ 2.80  
Range of warrant price per share, outstanding, end of period (in dollars per share) 2.80  
Range of warrant price per share, vested and exercisable at period end (in dollars per share) 2.80  
Weighted Average Exercise Price    
Weighted average exercise price, granted (in dollars per share) 2.80  
Weighted average exercise price, exercised (in dollars per share) 0  
Weighted average exercise price, expired (in dollars per share) 0  
Weighted average exercise price, outstanding, period end (in dollars per share) 2.80  
Weighted average exercise price, vested and exercisable, period end (in dollars per share) $ 2.80  
Weighted Average Remaining Contractual Life (Years)    
Weighted average remaining contractual life, balance (in years) 5 years 1 month 24 days 0 years
Weighted average remaining contractual life, granted (in years) 5 years 1 month 24 days  
Weighted average remaining contractual life, exercised (in years) 0 years  
Weighted average remaining contractual life, expired (in years) 0 years  
Weighted average remaining contractual life, vested and exercisable at period end (in years) 0 years  
February 2018 Warrants | Minimum    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Risk-free interest rate 2.71%  
Expected life (years) 4 years 7 months 17 days  
February 2018 Warrants | Maximum    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Risk-free interest rate 2.74%  
Expected life (years) 5 years 1 month 17 days  
2017 Warrants    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Risk-free interest rate 2.66%  
Volatility rate 80.00%  
Expected life (years) 3 years 7 months 13 days  
Dividend yield 0.00% 0.00%
Weighted Average Remaining Contractual Life (Years)    
Weighted average remaining contractual life, granted (in years) 0 years  
Weighted average remaining contractual life, exercised (in years) 0 years  
Weighted average remaining contractual life, expired (in years) 0 years  
2017 Warrants | Warrant    
Number of Shares Under Warrant    
Number of shares under warrant, balance at beginning of period 419,772  
Number of shares under warrant, granted 0  
Number of shares under warrant, exercised (9,752)  
Number of shares under warrant, expired 0  
Number of shares under warrant, balance at end of period 410,020 419,772
Number of shares under warrant, vested and exercisable at period end 410,020  
Range of warrant price per share, outstanding, end of period (in dollars per share) $ 1.50  
Range of warrant price per share, vested and exercisable at period end (in dollars per share) 1.50  
Weighted Average Exercise Price    
Weighted average exercise price, outstanding, period start (in dollars per share) 1.46  
Weighted average exercise price, granted (in dollars per share) 0  
Weighted average exercise price, exercised (in dollars per share) 1.50  
Weighted average exercise price, expired (in dollars per share) 0  
Weighted average exercise price, outstanding, period end (in dollars per share) 1.50  
Weighted average exercise price, vested and exercisable, period end (in dollars per share) $ 1.50  
Weighted Average Remaining Contractual Life (Years)    
Weighted average remaining contractual life, balance (in years) 3 years 7 months 17 days 4 years 4 months 17 days
Weighted average remaining contractual life, vested and exercisable at period end (in years) 3 years 7 months 17 days  
2017 Warrants | Minimum    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Risk-free interest rate   1.68%
Volatility rate   80.00%
Expected life (years)   6 months
2017 Warrants | Maximum    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Risk-free interest rate   1.86%
Volatility rate   160.11%
Expected life (years)   5 years