RELATED PARTY TRANSACTIONS (Details)		1 Months Ended				3 Months Ended	12 Months Ended
	Jan. 30, 2012 $ / shares shares	Jun. 30, 2019 USD ($)	Mar. 31, 2017 USD ($)	Jul. 31, 2016 USD ($)	Oct. 31, 2014 USD ($) ft²	Dec. 31, 2014	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Jan. 01, 2019 USD ($)	Apr. 30, 2018 USD ($)	Jul. 18, 2014 $ / shares
Related Party Transaction [Line Items]
Warrant purchase price | $ / shares												$ 100.00
Other Research and Development Expense							$ 151,934,000	$ 148,269,000	$ 149,793,000
Operating Lease Liability							12,081,000	11,834,000
Right-of-use-assets							9,312,000	9,402,000
Lfb Group [Member] | LFB License Agreement
Related Party Transaction [Line Items]
Other Research and Development Expense							6,000,000.0
Accounts payable related to LFB Biotechnologies							$ 0
LFB Biotechnologies [Member] | LFB License Agreement | Common Stock [Member]
Related Party Transaction [Line Items]
Commont stock issued | shares	5,000,000
Warrants issued to purchase common stock | shares	2,500,000
Warrant purchase price | $ / shares	$ 0.001
Office Agreement [Member]
Related Party Transaction [Line Items]
Percentage Of Occupancy					45.00%	45.00%	65.00%
Area of leases office space | ft²					24,000
Operating Lease Initial Commitment Period					15 years		15 years
Average Annual Rental Payments					$ 1,100,000		$ 1,400,000
Operating Lease Liability							12,100,000			$ 9,300,000
Right-of-use-assets							9,300,000			$ 7,700,000
Initial commitment period for office lease space					3 years
Long-term Line of Credit					$ 600,000
Additional collateral pledged											$ 600,000
Upfront licensing fee paid				$ 1,000,000.0
Expenses incurred			$ 200,000
Upfront fee							1,100,000	4,100,000
Shared Services Agreement [Member]
Related Party Transaction [Line Items]
Costs and Expenses, Related Party							$ 800,000	$ 900,000	1,600,000
Collaboration Agreement [Member]
Related Party Transaction [Line Items]
Upfront fee		$ 1,000,000.0							$ 600,000