Summary of Significant Accounting Policies - Convertible Senior Notes (Details) - USD ($) |
Dec. 31, 2019 |
Dec. 31, 2018 |
Jun. 30, 2017 |
Nov. 30, 2013 |
|---|---|---|---|---|
| 2022 Notes | ||||
| Debt Instrument [Line Items] | ||||
| Notes, par value | $ 782,491,000 | $ 782,500,000 | $ 782,500,000 | |
| Contractual interest rate, notes | 0.00% | |||
| 2018 Notes | ||||
| Debt Instrument [Line Items] | ||||
| Notes, par value | $ 575,000,000.0 | |||
| Contractual interest rate, notes | 0.00% |