CAPITALIZED FEES PAID TO A RELATED PARTY (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Capitalized Fees paid to a Related Party
Net carrying value	$ 125,253	$ 139,076
Weighted average remaining amortization period	9 years 1 month 6 days
Capitalized Fees paid to a Related Party, Future amortization
Estimated amortization expense for the year 2021	$ 13,800
Estimated amortization expense for the year 2022	13,800
Estimated amortization expense for the year 2023	13,800
Estimated amortization expense for the year 2024	13,800
Estimated amortization expense for the year 2025	13,800
Estimated amortization expense after 2025	56,300
GSK
Capitalized Fees paid to a Related Party
Gross carrying value	220,000	220,000
Accumulated amortization	(94,747)	(80,924)
Net carrying value	125,253	139,076
GSK | Royalty revenue from a related party
Capitalized Fees paid to a Related Party
Amortization expense	13,823	13,823	$ 13,823
GSK | United States
Capitalized Fees paid to a Related Party
Gross carrying value	120,000	120,000
GSK | Europe
Capitalized Fees paid to a Related Party
Gross carrying value	60,000	60,000
GSK | Japan
Capitalized Fees paid to a Related Party
Gross carrying value	$ 40,000	$ 40,000