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
Mar. 31, 2021
Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]    
Amortized cost $ 257,687 $ 324,567
Gross unrealized gains 5,317 1,302
Gross unrealized losses (16) (1,391)
Estimated fair value 262,988 324,478
Estimated fair value 307,354 363,567
Bank deposits    
Debt Securities, Available-for-sale [Line Items]    
Amortized cost 51,232 84,120
Gross unrealized gains 25 35
Gross unrealized losses (4) (1)
Estimated fair value 51,253 84,154
Corporate bonds    
Debt Securities, Available-for-sale [Line Items]    
Amortized cost 25,853 30,512
Gross unrealized gains 72 99
Gross unrealized losses (8) (1)
Estimated fair value 25,917 30,610
Agency bonds    
Debt Securities, Available-for-sale [Line Items]    
Amortized cost 4,501 4,499
Gross unrealized gains 0 2
Gross unrealized losses (4) 0
Estimated fair value 4,497 4,501
Commercial paper    
Debt Securities, Available-for-sale [Line Items]    
Amortized cost 19,815 45,459
Gross unrealized gains 9 27
Gross unrealized losses 0 (1)
Estimated fair value 19,824 45,485
Corporate equity securities    
Debt Securities, Available-for-sale [Line Items]    
Amortized cost 4,456 4,466
Gross unrealized gains 3,736 360
Gross unrealized losses 0 (1,388)
Estimated fair value 8,192 3,438
Mutual fund    
Debt Securities, Available-for-sale [Line Items]    
Amortized cost 151,830 151,512
Gross unrealized gains 53 386
Gross unrealized losses 0 0
Estimated fair value 151,883 151,898
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
Common Stock    
Debt Securities, Available-for-sale [Line Items]    
Estimated fair value 44,366 32,763
Warrants    
Debt Securities, Available-for-sale [Line Items]    
Amortized cost 0 0
Gross unrealized gains 1,422 393
Gross unrealized losses 0 0
Estimated fair value 1,422 393
Estimated fair value $ 0 $ 6,326