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, 2019 |
Dec. 31, 2018 |
Dec. 31, 2017 |
|
| Schedule Of Equity Method Investments [Line Items] | |||
| Investment in available-for-sale-securities | $ 189 | $ 192 | |
| Unrealized gain | $ 2 | ||
| Unrealized loss | $ (3) | $ (46) | |