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Investments - Available-for-sale Securities (Details) - USD ($)
$ in Thousands
Jun. 30, 2021
Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]    
Amortized Costs $ 13,467 $ 48,735
Gross Unrealized Holding Gains 5 89
Gross Unrealized Holding Losses 0 (6)
Fair Value 13,472 48,818
Commercial paper    
Debt Securities, Available-for-sale [Line Items]    
Amortized Costs 5,999 15,992
Gross Unrealized Holding Gains 0 2
Gross Unrealized Holding Losses 0 (3)
Fair Value 5,999 15,991
Corporate notes/bonds    
Debt Securities, Available-for-sale [Line Items]    
Amortized Costs 6,212 29,227
Gross Unrealized Holding Gains 1 72
Gross Unrealized Holding Losses 0 (3)
Fair Value 6,213 29,296
U.S. Treasuries    
Debt Securities, Available-for-sale [Line Items]    
Amortized Costs   2,251
Gross Unrealized Holding Gains   2
Gross Unrealized Holding Losses   0
Fair Value   2,253
U.S. Government agency securities    
Debt Securities, Available-for-sale [Line Items]    
Amortized Costs 1,256 1,265
Gross Unrealized Holding Gains 4 13
Gross Unrealized Holding Losses 0 0
Fair Value $ 1,260 $ 1,278