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Investments (Details) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2021 | Jun. 30, 2020 | Jun. 30, 2021 | Jun. 30, 2020
Schedule of Equity Method Investments [Line Items] |  |  |  |
Gain on interest in investment | $ 20,191 | $ 0 | $ 20,191 | $ 0
Mastery Logistics System, Inc. |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |
Initial value of ownership interest in investment | $ 5,000 |  | $ 5,000 |
Ownership interest in investment | 5.00% |  | 5.00% |
TuSimple |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |
Initial value of ownership interest in investment | $ 5,000 |  | $ 5,000 |
Gain on interest in investment | 20,191 |  | 20,191 |
Fair value of investment | $ 25,191 |  | $ 25,191 |

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