LICENSING ARRANGEMENTS (Details) - Licensing Agreements [Member]	3 Months Ended
	Mar. 31, 2017 USD ($)
CytomX [Member]
Licensing Arrangements [Line Items]
Number of additional targets added	$ 8
Number of original targets	4
R&D payments prior to 2017	75,000,000
License arrangement upfront payment	200,000,000
Potential contingent milestones	448,000,000
Biogen [Member]
Licensing Arrangements [Line Items]
Proceeds from out-licensed arrangements	300,000,000
Potential milestone receipts	410,000,000
Roche [Member]
Licensing Arrangements [Line Items]
Proceeds from out-licensed arrangements	170,000,000
Potential milestone receipts	$ 205,000,000