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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- Definition

Fair value portion of borrowing which can be exchanged for a specified number of another security at the option of the issuer or the holder, for example, but not limited to, the entity's common stock.

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- Definition

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