SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Revenue Recognition - License Revenue (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended	6 Months Ended	12 Months Ended
	Dec. 31, 2020	Jun. 30, 2021	Jun. 30, 2021	Dec. 31, 2020	May 31, 2021
Agreements
Revenue		$ 10,951	$ 16,334
License
Agreements
Revenue		2,000	2,000
License | Development and commercialization arrangement | SciClone
Agreements
Revenue		0	0	$ 20,000
Amount of milestone achieved		0	0
Upfront payment	$ 20,000
Maximum regulatory milestones	40,000			40,000
Maximum sales-based milestones	$ 60,000			$ 60,000
License | Development and commercialization arrangement | Adium
Agreements
Upfront payment		$ 2,000	$ 2,000
Maximum regulatory milestones					$ 3,500