v3.19.3

FAIR VALUE OF FINANCIAL INSTRUMENTS - Fair Value of Convertible Senior Notes (Details) - Level 2 - Fair Value, Measurements, Recurring - USD ($) $ in Thousands | Sep. 30, 2019 | Dec. 31, 2018
--- | --- | ---
Carrying Value |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Convertible senior notes | $ 928,869 | $ 899,695
Fair Value (Level 2) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Convertible senior notes | 1,536,753 | 1,417,161
2023 Notes | Carrying Value |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Convertible senior notes | 740,921 | 718,522
2023 Notes | Fair Value (Level 2) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Convertible senior notes | 961,092 | 901,468
2022 Notes | Carrying Value |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Convertible senior notes | 187,948 | 181,173
2022 Notes | Fair Value (Level 2) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Convertible senior notes | $ 575,661 | $ 515,693

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