Quarterly report pursuant to Section 13 or 15(d)

Basis of Presentation and Summary of Significant Accounting Policies - Investment Categories (Details)

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Basis of Presentation and Summary of Significant Accounting Policies - Investment Categories (Details) - USD ($)
$ in Thousands
Sep. 30, 2021
Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]    
Amortized cost $ 257,266 $ 324,567
Gross unrealized gains 1,070 1,302
Gross unrealized losses (726) (1,391)
Estimated fair value 257,610 324,478
Estimated fair value 299,781 363,567
Bank deposits    
Debt Securities, Available-for-sale [Line Items]    
Amortized cost 47,739 84,120
Gross unrealized gains 8 35
Gross unrealized losses (3) (1)
Estimated fair value 47,744 84,154
Corporate bonds    
Debt Securities, Available-for-sale [Line Items]    
Amortized cost 25,914 30,512
Gross unrealized gains 50 99
Gross unrealized losses 0 (1)
Estimated fair value 25,964 30,610
Agency bonds    
Debt Securities, Available-for-sale [Line Items]    
Amortized cost 2,501 4,499
Gross unrealized gains 0 2
Gross unrealized losses 0 0
Estimated fair value 2,501 4,501
Commercial paper    
Debt Securities, Available-for-sale [Line Items]    
Amortized cost 23,264 45,459
Gross unrealized gains 10 27
Gross unrealized losses 0 (1)
Estimated fair value 23,274 45,485
Corporate equity securities    
Debt Securities, Available-for-sale [Line Items]    
Amortized cost 5,807 4,466
Gross unrealized gains 307 360
Gross unrealized losses (723) (1,388)
Estimated fair value 5,391 3,438
Mutual fund    
Debt Securities, Available-for-sale [Line Items]    
Amortized cost 152,041 151,512
Gross unrealized gains 53 386
Gross unrealized losses 0 0
Estimated fair value 152,094 151,898
Treasury bill    
Debt Securities, Available-for-sale [Line Items]    
Amortized cost 0 3,999
Gross unrealized gains 0 0
Gross unrealized losses 0 0
Estimated fair value 0 3,999
Warrants    
Debt Securities, Available-for-sale [Line Items]    
Amortized cost 0 0
Gross unrealized gains 642 393
Gross unrealized losses 0 0
Estimated fair value 642 393
Estimated fair value 0 6,326
Common Stock    
Debt Securities, Available-for-sale [Line Items]    
Estimated fair value $ 42,171 $ 32,763