Stockholders' Equity - Allocation Of Proceeds (Details) - Interstate Battery System International, Inc. and Other Investors $ in Thousands  | 
12 Months Ended | 
|---|---|
| 
 Dec. 31, 2018  
USD ($) 
 | |
| Class of Stock [Line Items] | |
| Fair value | $ 26,463 | 
| Allocated value | 10,000 | 
| Convertible Note | |
| Class of Stock [Line Items] | |
| Fair value | 4,879 | 
| Allocated value | 1,844 | 
| Warrant | |
| Class of Stock [Line Items] | |
| Fair value | 13,586 | 
| Allocated value | 5,134 | 
| Common Stock | |
| Class of Stock [Line Items] | |
| Fair value | 7,998 | 
| Allocated value | $ 3,022 | 
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