Investments in affiliates and investments in available-for-sale securities - Investments in available-for-sale securities (Details) - USD ($) $ in Thousands |
12 Months Ended | |
|---|---|---|
Dec. 31, 2020 |
Dec. 31, 2019 |
|
| Schedule Of Equity Method Investments [Line Items] | ||
| Investment in available-for-sale-securities | $ 222 | $ 189 |
| Unrealized gain | 33 | |
| Unrealized loss | $ (3) | $ (46) |