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Investments, Available-for-Sale - Schedule of Cost, Gross Unrealized Holding Gains, Gross Unrealized Holding Losses and Fair Value of Available for Sale Investments (Details) - USD ($)
$ in Thousands
Sep. 30, 2021
Dec. 31, 2020
Short-term Investments    
Schedule Of Available For Sale Securities [Line Items]    
Investments, available-for-sale, Amortized Cost $ 48,392 $ 215,185
Investments, available-for-sale, Unrealized Gains 1  
Investments, available-for-sale, Unrealized Losses   (31)
Investments, available-for-sale, Estimated Fair Value 48,393 215,154
Long Term Investments    
Schedule Of Available For Sale Securities [Line Items]    
Investments, available-for-sale, Amortized Cost 6,959  
Investments, available-for-sale, Unrealized Losses (3)  
Investments, available-for-sale, Estimated Fair Value 6,956  
U.S. Treasury Securities | Short-term Investments    
Schedule Of Available For Sale Securities [Line Items]    
Investments, available-for-sale, Amortized Cost 47,656 215,185
Investments, available-for-sale, Unrealized Gains 1  
Investments, available-for-sale, Unrealized Losses   (31)
Investments, available-for-sale, Estimated Fair Value 47,657 $ 215,154
U.S. Treasury Securities | Long Term Investments    
Schedule Of Available For Sale Securities [Line Items]    
Investments, available-for-sale, Amortized Cost 6,006  
Investments, available-for-sale, Unrealized Losses (3)  
Investments, available-for-sale, Estimated Fair Value 6,003  
Certificates of deposit | Short-term Investments    
Schedule Of Available For Sale Securities [Line Items]    
Investments, available-for-sale, Amortized Cost 736  
Investments, available-for-sale, Estimated Fair Value 736  
Certificates of deposit | Long Term Investments    
Schedule Of Available For Sale Securities [Line Items]    
Investments, available-for-sale, Amortized Cost 953  
Investments, available-for-sale, Estimated Fair Value $ 953