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, 2020
Dec. 31, 2019
Equity Securities, FV-NI [Abstract]    
Estimated fair value $ 4,621 $ 9,910
Debt and Equity Securities, FV-NI [Abstract]    
Amortized cost 630,227 941,174
Gross unrealized gains 671 933
Gross unrealized losses (9,614) (2,118)
Estimated fair value 621,284 939,989
Bank deposits    
Debt Securities, Available-for-sale [Line Items]    
Amortized cost 284,855 411,690
Gross unrealized gains 157 188
Gross unrealized losses (1,398) (3)
Estimated fair value 283,614 411,875
Corporate bonds    
Debt Securities, Available-for-sale [Line Items]    
Amortized cost 62,191 63,818
Gross unrealized gains 21 161
Gross unrealized losses (1,666) 0
Estimated fair value 60,546 63,979
Commercial paper    
Debt Securities, Available-for-sale [Line Items]    
Amortized cost 127,928 210,525
Gross unrealized gains 5 43
Gross unrealized losses (273) (16)
Estimated fair value 127,660 210,552
Corporate equity securities    
Debt Securities, Available-for-sale [Line Items]    
Amortized cost 4,506 4,506
Gross unrealized gains 430 416
Gross unrealized losses (3,483) (1,850)
Estimated fair value 1,453 3,072
Mutual fund    
Debt Securities, Available-for-sale [Line Items]    
Amortized cost 150,747 250,635
Gross unrealized gains 0 0
Gross unrealized losses (2,794) (249)
Estimated fair value 147,953 250,386
Warrants    
Equity Securities, FV-NI [Abstract]    
Amortized cost 0 0
Gross unrealized gains 58 125
Gross unrealized losses 0 0
Estimated fair value $ 58 $ 125