Nature of Business and Accounting Policies - Schedule of Cash, Cash Equivalents, and Restricted Cash (Details) - USD ($) $ in Thousands |
Dec. 31, 2019 |
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
|---|---|---|---|---|
| Accounting Policies [Abstract] | ||||
| Cash and cash equivalents | $ 3,109,322 | $ 2,650,134 | $ 1,665,412 | $ 1,183,945 |
| Prepaid expenses and other current assets | 8,004 | 4,910 | 2,114 | 47,762 |
| Other assets | 3,355 | 3,209 | 0 | 0 |
| Cash, cash equivalents and restricted cash per statement of cash flows | $ 3,120,681 | $ 2,658,253 | $ 1,667,526 | $ 1,231,707 |