Quarterly report pursuant to Section 13 or 15(d)

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Revenue Recognition Narrative (Details)

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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Revenue Recognition Narrative (Details) - USD ($)
1 Months Ended 3 Months Ended 9 Months Ended
May 31, 2018
Mar. 31, 2015
Sep. 30, 2020
Sep. 30, 2019
Sep. 30, 2020
Sep. 30, 2019
Dec. 31, 2019
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]              
Revenue recognized     $ 142,000 $ 1,183,000 $ 1,795,000 $ 7,248,000  
Deferred revenue     0   $ 0   $ 1,795,000
Collaborative Arrangement              
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]              
Non-refundable upfront fees $ 15,600,000 $ 11,000,000.0          
Development milestone payments   10,000,000.0          
Commercialization milestone payments   $ 30,000,000.0          
Basis point reduction         1.50%    
Revenue recognized     100,000 $ 1,200,000 $ 1,800,000 $ 7,200,000  
Deferred revenue     $ 0   0   $ 1,800,000
Milestone payment received         $ 10,000,000.0