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MAJOR CUSTOMERS, PARTNERSHIPS AND STRATEGIC ALLIANCES - Biogen MA, Inc. (Detail)
$ / shares in Units, $ in Thousands
 1 Months Ended 3 Months Ended 9 Months Ended 12 Months Ended
May 31, 2020
USD ($)
Apr. 30, 2020
USD ($)
product_target
$ / shares
shares
Sep. 30, 2022
USD ($)
Sep. 30, 2021
USD ($)
Sep. 30, 2022
USD ($)
Sep. 30, 2021
USD ($)
Dec. 31, 2020
USD ($)
Dec. 31, 2021
USD ($)
Research and Development Arrangement, Contract to Perform for Others [Line Items]                
Accounts receivable     $ 4,522   $ 4,522     $ 6,013
Biogen MA, Inc. | Stock purchase agreement                
Research and Development Arrangement, Contract to Perform for Others [Line Items]                
Number of shares issued in transaction (in shares) | shares   24,420,157            
Sale of stock, price per share (in dollars per share) | $ / shares   $ 9.2137            
Consideration received on transaction   $ 225,000            
Standstill restriction period   3 years            
Standstill restriction, ownership threshold percentage ownership percentage   5.00%            
Collaborative arrangement transaction price   $ 204,600            
Excess consideration received on transaction   79,600            
Collaboration agreement, equity issued   145,400            
Accounts receivable     1,700   1,700     2,800
Deferred revenue     132,100   132,100     $ 154,000
Recognized portion of equity issued             $ 2,900  
Biogen MA, Inc. | Collaboration And License Agreement                
Research and Development Arrangement, Contract to Perform for Others [Line Items]                
Consideration received on transaction   204,600            
Proceeds from collaborators $ 125,000 125,000            
Maximum milestone payment receivable   $ 2,400,000            
Number of additional product targets | product_target   7            
Remaining period   5 years            
Number of product targets selected | product_target   3            
Research period   7 years            
Maximum number of product targets replaced | product_target   10            
Financial advisory fees             $ 7,000  
Percent of initial recognition   2.00%            
Portion of contract asset recognized     4,100   4,100      
Amortization     $ 100 $ 100 $ 400 $ 400    
Biogen MA, Inc. | Collaboration And License Agreement | Pre-approval milestone                
Research and Development Arrangement, Contract to Perform for Others [Line Items]                
Maximum milestone payment receivable   $ 925,000            
Biogen MA, Inc. | Collaboration And License Agreement | Sales-based milestone                
Research and Development Arrangement, Contract to Perform for Others [Line Items]                
Maximum milestone payment receivable   $ 1,500,000