FAIR VALUE OF FINANCIAL INSTRUMENTS - Schedule of Fair Value and Carrying Value of Convertible Senior Notes (Details) - Fair Value, Measurements, Recurring - Level 2 - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Carrying Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	$ 938,832	$ 899,695
Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	1,541,333	1,417,161
2023 Notes | Carrying Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	748,564	718,522
2023 Notes | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	962,516	901,468
2022 Notes | Carrying Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	190,268	181,173
2022 Notes | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	$ 578,817	$ 515,693