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Fair Value Measurements - Narrative (Details) - USD ($) | Dec. 31, 2020 | Aug. 21, 2020 | Dec. 31, 2019 | Mar. 31, 2017
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Non-financial Assets | Fair Value, Measurements, Nonrecurring |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Non-financial assets | $ 0 |  | $ 0 |
Notes Payable | 3.875% Notes |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Debt instrument, interest rate | 3.875% | 3.875% |  |
Convertible Debt | 1.00% Notes |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Debt instrument, interest rate | 1.00% |  |  |
Convertible Debt | 1.625% Notes |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Debt instrument, interest rate | 1.625% |  | 1.625% | 1.625%

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- Definition Contractual interest rate for funds borrowed, under the debt agreement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(1)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
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