COLLABORATIVE RESEARCH AND LICENSE AGREEMENTS - Summary of Deferred Revenue Balances (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
CURRENT	$ 200,041	$ 212,258
NONCURRENT	268,502	182,730
TOTAL	468,543	394,988
Novo
Disaggregation of Revenue [Line Items]
CURRENT	39,672	813
NONCURRENT	131,896	3,359
TOTAL	171,568	4,172
Roche
Disaggregation of Revenue [Line Items]
CURRENT	83,655	118,094
NONCURRENT	61,270	81,906
TOTAL	144,925	200,000
Lilly
Disaggregation of Revenue [Line Items]
CURRENT	51,088	63,233
NONCURRENT	53,522	72,314
TOTAL	104,610	135,547
Alexion
Disaggregation of Revenue [Line Items]
CURRENT	25,520	27,845
NONCURRENT	21,814	25,151
TOTAL	47,334	52,996
BI
Disaggregation of Revenue [Line Items]
CURRENT	106	2,273
NONCURRENT	0	0
TOTAL	$ 106	$ 2,273