Investment in affiliates and available-for-sale securities - AFS Securities (Details) - USD ($) $ in Thousands |
3 Months Ended | 6 Months Ended | 12 Months Ended | |||
|---|---|---|---|---|---|---|
Jun. 30, 2019 |
Jun. 30, 2018 |
Jun. 30, 2019 |
Jun. 30, 2018 |
Dec. 31, 2017 |
Dec. 31, 2018 |
|
| Schedule Of Equity Method Investments [Line Items] | ||||||
| Investment in available-for-sale-securities | $ 193 | $ 193 | $ 192 | |||
| Unrealized loss | $ 25 | $ 27 | ||||
| Unrealized gain | $ 19 | $ 1 | $ 2 | |||