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RESEARCH AND LICENSE AGREEMENTS WITH PRINCETON UNIVERSITY, UNIVERSITY OF SOUTHERN CALIFORNIA AND THE UNIVERSITY OF MICHIGAN - Additional Information (Details) - USD ($)
 3 Months Ended 6 Months Ended
Jun. 30, 2020
Jun. 30, 2019
Jun. 30, 2020
Jun. 30, 2019
Research and Development Arrangement, Contract to Perform for Others [Line Items]        
Royalty expense $ 1,618,000 $ 3,454,000 $ 4,902,000 $ 5,991,000
1997 Amended License Agreement [Member]        
Research and Development Arrangement, Contract to Perform for Others [Line Items]        
Royalty expense 1,600,000 3,500,000 $ 4,900,000 $ 6,000,000.0
Royalty rate for licensed products sold by the Company (in hundredths)       3.00%
Royalty rate for licensed products sold by the Company's sublicenses (in hundredths)       3.00%
2006 Research Agreement [Member]        
Research and Development Arrangement, Contract to Perform for Others [Line Items]        
Research agreement, extension term (in years)     2 years  
Research agreement, new amendment expiration date     Apr. 30, 2023  
Maximum obligation 9,000,000.0   $ 9,000,000.0  
Research and development expense incurred $ 304,000 $ 260,000 $ 581,000 $ 503,000