DEBT - Interest Expense (Details) - Convertible debt - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended
	Feb. 29, 2020	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Debt Instrument [Line Items]
Interest rate	0.75%
Contractual interest expense (0.75% coupon)		$ 1,125	$ 1,125	$ 2,250	$ 1,575
Amortization of debt discount		0	3,757	0	5,253
Amortization of issuance costs		675	558	1,348	780
Interest expense		$ 1,800	$ 5,440	$ 3,598	$ 7,608
Weighted-average effective interest rate		1.20%	4.30%	1.20%	4.30%