COLLABORATIVE RESEARCH AND LICENSE AGREEMENTS - Summary of Revenue Recognized (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Revenue	$ 48,875	$ 8,035	$ 123,351	$ 16,824
Novo
Disaggregation of Revenue [Line Items]
Revenue	3,552	0	7,604	0
Roche
Disaggregation of Revenue [Line Items]
Revenue	18,686	0	58,670	0
Lilly
Disaggregation of Revenue [Line Items]
Revenue	12,073	5,274	31,142	8,346
Alexion
Disaggregation of Revenue [Line Items]
Revenue	13,639	1,451	23,464	2,954
BI
Disaggregation of Revenue [Line Items]
Revenue	$ 925	$ 1,310	$ 2,471	$ 5,524