Quarterly report pursuant to Section 13 or 15(d)

Basis of Presentation and Summary of Significant Accounting Policies - Available-for-Sale Debt Securities in an Unrealized Loss Position (Details)

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Basis of Presentation and Summary of Significant Accounting Policies - Available-for-Sale Debt Securities in an Unrealized Loss Position (Details) - USD ($)
Sep. 30, 2020
Dec. 31, 2019
Gross Unrealized Losses    
Less than 12 months $ (400) $ (19,000)
12 months or greater 0 0
Total (400) (19,000)
Estimated Fair Value    
Less than 12 months 8,018,000 137,947,000
12 months or greater 0 0
Total 8,018,000 137,947,000
Bank deposits    
Gross Unrealized Losses    
Less than 12 months 0 (3,000)
12 months or greater 0 0
Total 0 (3,000)
Estimated Fair Value    
Less than 12 months 5,011,000 58,584,000
12 months or greater 0 0
Total 5,011,000 58,584,000
Corporate bonds    
Gross Unrealized Losses    
Less than 12 months (400)  
12 months or greater 0  
Total (400)  
Estimated Fair Value    
Less than 12 months 3,007,000  
12 months or greater 0  
Total $ 3,007,000  
Commercial paper    
Gross Unrealized Losses    
Less than 12 months   (16,000)
12 months or greater   0
Total   (16,000)
Estimated Fair Value    
Less than 12 months   79,363,000
12 months or greater   0
Total   $ 79,363,000