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Description of Business - Additional Information (Detail) - USD ($)
$ in Thousands
Dec. 31, 2020
Nov. 30, 2020
Dec. 31, 2019
Aug. 31, 2019
Aug. 06, 2019
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]          
Accumulated deficit $ (3,049,143)   $ (2,991,903)    
Principal amount 122,900        
Cash and cash equivalents 67,005   29,906    
MidCap Credit Facility          
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]          
Principal amount 50,000   40,000    
Principal amount       $ 75,000  
Amount outstanding     $ 50,000    
Amount available under credit facility 25,000     25,000  
Minimum cash covenant   $ 30,000     $ 30,000
MidCap Credit Facility | Tranche 2          
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]          
Amount available under credit facility       $ 10,000  
Minimum cash covenant $ 30,000