Marketable Investment Securities - Equity Securities (Details) - USD ($) $ in Thousands |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2020 |
Jun. 30, 2019 |
Jun. 30, 2020 |
Jun. 30, 2019 |
|
| Investments, Debt and Equity Securities [Abstract] | ||||
| Proceeds from sales | $ 4,719 | $ 29,051 | $ 4,853 | $ 79,928 |
| Gains (losses) on investments, net | $ 2,512 | $ 13,028 | $ (8,603) | $ 43,277 |