Annual report pursuant to Section 13 and 15(d)

Stockholders' Equity - Black-Scholes-Merton Option Pricing Model (Details)

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Stockholders' Equity - Black-Scholes-Merton Option Pricing Model (Details) - USD ($)
$ / shares in Units, $ in Thousands
 12 Months Ended
Dec. 31, 2018
May 24, 2016
Class of Stock [Line Items]    
Market price   $ 11.39
Warrant Exercise Price (in dollars per share) $ 6.00  
Warrant 1 | Interstate Battery System International, Inc.    
Class of Stock [Line Items]    
Warrant shares issued (in shares) 702,247  
Market price $ 11.39  
Warrant Exercise Price (in dollars per share) $ 7.12  
Term (years) 2 years  
Risk-free interest rate 0.91%  
Volatility 65.70%  
Dividend rate 0.00%  
Per share FV of warrant $ 5.89  
FV of warrant $ 4,136  
Warrant 2 | Interstate Battery System International, Inc.    
Class of Stock [Line Items]    
Warrant shares issued (in shares) 1,605,131  
Market price $ 11.39  
Warrant Exercise Price (in dollars per share) $ 9.00  
Term (years) 3 years  
Risk-free interest rate 1.05%  
Volatility 67.80%  
Dividend rate 0.00%  
Per share FV of warrant $ 5.89  
FV of warrant $ 9,450