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, 2020
Dec. 31, 2019
Equity Securities, FV-NI [Abstract]    
Estimated fair value $ 6,581 $ 9,910
Debt and Equity Securities, FV-NI [Abstract]    
Amortized cost 299,291 941,174
Gross unrealized gains 1,037 933
Gross unrealized losses (2,624) (2,118)
Estimated fair value 297,704 939,989
Bank deposits    
Debt Securities, Available-for-sale [Line Items]    
Amortized cost 68,226 411,690
Gross unrealized gains 101 188
Gross unrealized losses 0 (3)
Estimated fair value 68,327 411,875
Corporate bonds    
Debt Securities, Available-for-sale [Line Items]    
Amortized cost 27,125 63,818
Gross unrealized gains 102 161
Gross unrealized losses 0 0
Estimated fair value 27,227 63,979
Commercial paper    
Debt Securities, Available-for-sale [Line Items]    
Amortized cost 47,943 210,525
Gross unrealized gains 60 43
Gross unrealized losses 0 (16)
Estimated fair value 48,003 210,552
Corporate equity securities    
Debt Securities, Available-for-sale [Line Items]    
Amortized cost 4,484 4,506
Gross unrealized gains 415 416
Gross unrealized losses (2,624) (1,850)
Estimated fair value 2,275 3,072
Mutual fund    
Debt Securities, Available-for-sale [Line Items]    
Amortized cost 151,513 250,635
Gross unrealized gains 204 0
Gross unrealized losses 0 (249)
Estimated fair value 151,717 250,386
Warrants    
Equity Securities, FV-NI [Abstract]    
Amortized cost 0 0
Gross unrealized gains 155 125
Gross unrealized losses 0 0
Estimated fair value $ 155 $ 125