CONVERTIBLE NOTES - Schedule of Underlying Equity and Liability Allocation of Transaction Costs (Details) - USD ($) $ in Thousands	Feb. 29, 2020	Mar. 08, 2019	Jun. 12, 2018	Jan. 17, 2018
January 2025 Notes
Long-term debt
Transaction costs allocated to liability component				$ 13,569
Transaction costs allocated to equity component				5,340
Total transaction costs				$ 18,909
June 2025 Notes
Long-term debt
Transaction costs allocated to liability component			$ 5,052
Transaction costs allocated to equity component			2,311
Total transaction costs			$ 7,363
2027 Convertible notes
Long-term debt
Transaction costs allocated to liability component		$ 11,395
Transaction costs allocated to equity component		6,632
Total transaction costs		$ 18,027
2028 Convertible notes
Long-term debt
Transaction costs allocated to liability component	$ 16,811
Transaction costs allocated to equity component	7,642
Total transaction costs	$ 24,453