Marketable Investment Securities - Equity Securities (Details) - USD ($) $ in Thousands |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Sep. 30, 2020 |
Sep. 30, 2019 |
Sep. 30, 2020 |
Sep. 30, 2019 |
|
| Investments, Debt and Equity Securities [Abstract] | ||||
| Proceeds from sales | $ 9,493 | $ 22,847 | $ 14,346 | $ 102,775 |
| Gains (losses) on investments, net | $ 68 | $ 8,473 | $ (8,535) | $ 51,750 |