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Marketable Securities (Details) - USD ($)
12 Months Ended
Dec. 31, 2019
Sep. 30, 2020
Debt Securities, Available-for-sale [Line Items]    
Amortized Cost $ 89,268,000 $ 79,019,000
Gross Unrealized Gains 26,000 3,000
Gross Unrealized Losses (10,000) 0
Fair Value 89,284,000 79,022,000
Allowance for credit loss related to available-for-sale debt securities   0
Losses related to other-than-temporary impairments of available-for-sale debt securities 0  
U.S. Treasury securities    
Debt Securities, Available-for-sale [Line Items]    
Amortized Cost   60,003,000
Gross Unrealized Gains   2,000
Gross Unrealized Losses   0
Fair Value   60,005,000
Government-sponsored enterprises    
Debt Securities, Available-for-sale [Line Items]    
Amortized Cost 13,216,000 14,006,000
Gross Unrealized Gains 6,000 1,000
Gross Unrealized Losses 0 0
Fair Value 13,222,000 14,007,000
Corporate debt securities    
Debt Securities, Available-for-sale [Line Items]    
Amortized Cost 76,052,000 5,010,000
Gross Unrealized Gains 20,000 0
Gross Unrealized Losses (10,000) 0
Fair Value $ 76,062,000 $ 5,010,000