Marketable Investment Securities - Schedule of Unrealized Gains (Losses) on Available-for-Sale Securities (Details) - USD ($) $ in Thousands |
Sep. 30, 2020 |
Dec. 31, 2019 |
|---|---|---|
| Debt Securities, Available-for-sale [Line Items] | ||
| Debt securities | $ 1,906,945 | $ 904,022 |
| Corporate bonds | ||
| Debt Securities, Available-for-sale [Line Items] | ||
| Amortized Cost | 305,628 | 567,926 |
| Unrealized Gains | 152 | 518 |
| Unrealized Losses | (5) | (2) |
| Debt securities | 305,775 | 568,442 |
| Commercial paper | ||
| Debt Securities, Available-for-sale [Line Items] | ||
| Amortized Cost | 1,330,726 | 321,705 |
| Unrealized Gains | 0 | 1 |
| Unrealized Losses | 0 | 0 |
| Debt securities | 1,330,726 | 321,706 |
| Other debt securities | ||
| Debt Securities, Available-for-sale [Line Items] | ||
| Amortized Cost | 270,433 | 13,867 |
| Unrealized Gains | 11 | 7 |
| Unrealized Losses | 0 | 0 |
| Debt securities | 270,444 | 13,874 |
| Total available-for-sale debt securities | ||
| Debt Securities, Available-for-sale [Line Items] | ||
| Amortized Cost | 1,906,787 | 903,498 |
| Unrealized Gains | 163 | 526 |
| Unrealized Losses | (5) | (2) |
| Debt securities | $ 1,906,945 | $ 904,022 |