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Investments and Fair Value of Financial Instruments - Gains and Losses of Marketable Investments (Details) - USD ($)
$ in Thousands
Mar. 31, 2021
Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]    
Amortized Cost $ 186,489 $ 194,320
Gross Unrealized Gains 553 846
Gross Unrealized Losses (65) (4)
Allowance for Credit Loss 0 0
Fair Value 186,977 195,162
Commercial paper    
Debt Securities, Available-for-sale [Line Items]    
Amortized Cost 4,247 4,242
Gross Unrealized Gains 2 4
Gross Unrealized Losses 0 0
Allowance for Credit Loss 0 0
Fair Value 4,249 4,246
U.S. agency and government sponsored securities    
Debt Securities, Available-for-sale [Line Items]    
Amortized Cost 4,548 7,846
Gross Unrealized Gains 7 11
Gross Unrealized Losses 0 0
Allowance for Credit Loss 0 0
Fair Value 4,555 7,857
U.S. states and municipalities    
Debt Securities, Available-for-sale [Line Items]    
Amortized Cost 47,283 47,934
Gross Unrealized Gains 148 162
Gross Unrealized Losses (6) (1)
Allowance for Credit Loss 0 0
Fair Value 47,425 48,095
Corporate bonds    
Debt Securities, Available-for-sale [Line Items]    
Amortized Cost 130,411 134,298
Gross Unrealized Gains 396 669
Gross Unrealized Losses (59) (3)
Allowance for Credit Loss 0 0
Fair Value $ 130,748 $ 134,964