Marketable Securities and Equity Investments - Available-for-Sale Debt Securities by Contractual Maturity (Details) - USD ($) $ in Thousands |
Dec. 31, 2019 |
Dec. 31, 2018 |
|---|---|---|
| Investments, Debt and Equity Securities [Abstract] | ||
| Matures within one year | $ 1,137,942 | $ 1,647,500 |
| Matures after one year through five years | 105,527 | 1,245 |
| Total | $ 1,243,469 | $ 1,648,745 |