Annual report pursuant to Section 13 and 15(d)

Cash Equivalents and Marketable Securities - Schedule of Cash Equivalents and Marketable Securities (Details)

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Cash Equivalents and Marketable Securities - Schedule of Cash Equivalents and Marketable Securities (Details) - USD ($)
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Cash And Cash Equivalents [Line Items]      
Amortized Cost Basis $ 324,845,000 $ 131,499,000  
Unrealized Gains 131,000 168,000  
Unrealized Losses (3,000) (3,000)  
Fair Value 324,973,000 131,664,000  
Less amounts classified as cash equivalents, Amortized Cost Basis (206,152,000) (4,960,000) $ (125,298,000)
Marketable Securities      
Cash And Cash Equivalents [Line Items]      
Amortized Cost Basis 120,213,000 128,348,000  
Unrealized Gains 131,000 168,000  
Unrealized Losses (3,000) (3,000)  
Fair Value 120,341,000 128,513,000  
Cash Equivalents      
Cash And Cash Equivalents [Line Items]      
Less amounts classified as cash equivalents, Amortized Cost Basis (204,632,000) (3,151,000)  
Less amounts classified as cash equivalents, Fair Value (204,632,000) (3,151,000)  
Money Market Funds      
Cash And Cash Equivalents [Line Items]      
Amortized Cost Basis 204,632,000 3,151,000  
Unrealized Gains 0 0  
Unrealized Losses 0 0  
Fair Value 204,632,000 3,151,000  
Commercial Paper      
Cash And Cash Equivalents [Line Items]      
Amortized Cost Basis 42,208,000 4,952,000  
Unrealized Gains 0 0  
Unrealized Losses 0 0  
Fair Value 42,208,000 4,952,000  
Corporate Debt Securities      
Cash And Cash Equivalents [Line Items]      
Amortized Cost Basis 25,669,000 69,423,000  
Unrealized Gains 48,000 79,000  
Unrealized Losses (1,000) (3,000)  
Fair Value 25,716,000 69,499,000  
Asset-backed Securities      
Cash And Cash Equivalents [Line Items]      
Amortized Cost Basis 12,593,000 27,005,000  
Unrealized Gains 39,000 50,000  
Unrealized Losses 0 0  
Fair Value 12,632,000 27,055,000  
U.S. Government Securities      
Cash And Cash Equivalents [Line Items]      
Amortized Cost Basis 39,743,000 26,968,000  
Unrealized Gains 44,000 39,000  
Unrealized Losses (2,000) 0  
Fair Value $ 39,785,000 $ 27,007,000