v3.20.2

Weichai Transactions (Details) - USD ($) |  |  |  | 1 Months Ended | 3 Months Ended | 9 Months Ended |
--- | --- | --- | --- | --- | --- | --- | ---
Apr. 23, 2019 | Oct. 01, 2018 | Mar. 20, 2017 | Sep. 30, 2018 | Sep. 30, 2020 | Sep. 30, 2019 | Sep. 30, 2020 | Sep. 30, 2019 | Dec. 31, 2019
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |
Exercise proceeds for the warrants |  |  |  |  |  |  | $ 0 | $ 1,616,000 |
Term of collaborative arrangement |  |  | 3 years |  |  |  |  |  |
Extension term of collaborative arrangement |  |  | 3 years |  |  |  |  |  |
Purchased inventory |  |  |  |  | $ 4,100,000 | $ 600,000 | 16,300,000 | 1,500,000 |
Outstanding payables |  |  |  |  | $ 6,600,000 |  | $ 6,600,000 |  | $ 5,900,000
Share Purchase Agreement, Weichai Transaction |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |
Exercisable (term) |  |  |  | 90 days |  |  |  |  |
Volume weighted average share price percentage |  | 50.00% |  |  |  |  |  |  |
Trading period | 20 days | 20 days |  |  |  |  |  |  |
Aggregate amount (up to) |  | $ 15,000,000.0 |  |  |  |  |  |  |
Expense as a result of the exercise |  |  |  |  |  |  |  | $ 1,400,000 |
Share Purchase Agreement, Second Amended and Restated Warrant | Series B |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |
Exercise of private placement warrants (in shares) | 4,049,759 |  |  |  |  |  |  |  |
Percent ownership of outstanding common stock | 51.50% |  |  |  |  |  |  |  |
Exercise proceeds for the warrants | $ 1,600,000 |  |  |  |  |  |  |  |

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