DEBT - Schedule of Debt (Details) - Unsecured Debt - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020	Jul. 31, 2020	Mar. 31, 2017
Convertible Senior Notes Due 2025
Debt Instrument [Line Items]
Stated interest rate (as a percent)	0.75%		0.75%
Convertible senior notes, gross	$ 402,500	$ 402,500
Deferred financing costs	(8,058)	(8,940)
Discount on debt	(72,734)	(80,530)
Total debt, net of debt discount and deferred financing costs	$ 321,708	313,030
Convertible Senior Notes Due 2022
Debt Instrument [Line Items]
Stated interest rate (as a percent)	2.375%		2.375%	2.375%
Convertible senior notes, gross	$ 160,000	160,000
Deferred financing costs	(661)	(1,089)
Discount on debt	(5,658)	(9,263)
Total debt, net of debt discount and deferred financing costs	$ 153,681	$ 149,648