Quarterly report pursuant to Section 13 or 15(d)

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

v3.19.2
Basis of Presentation and Summary of Significant Accounting Policies - Investment Categories (Details) - USD ($)
$ in Thousands
Jun. 30, 2019
Dec. 31, 2018
Equity Securities, FV-NI [Abstract]    
Estimated fair value $ 10,260 $ 9,257
Debt and Equity Securities, FV-NI [Abstract]    
Amortized cost 1,057,454 600,154
Gross unrealized gains 1,796 1,226
Gross unrealized losses (248) (163)
Estimated fair value 1,059,002 601,217
Bank deposits    
Debt Securities, Available-for-sale [Line Items]    
Amortized cost 582,991 311,066
Gross unrealized gains 462 26
Gross unrealized losses (13) (29)
Estimated fair value 583,440 311,063
Corporate bonds    
Debt Securities, Available-for-sale [Line Items]    
Amortized cost 46,360 53,223
Gross unrealized gains 160 1
Gross unrealized losses 0 (45)
Estimated fair value 46,520 53,179
Commercial paper    
Debt Securities, Available-for-sale [Line Items]    
Amortized cost 423,578 225,731
Gross unrealized gains 246 8
Gross unrealized losses (19) (76)
Estimated fair value 423,805 225,663
U.S. Government bonds    
Debt Securities, Available-for-sale [Line Items]    
Amortized cost 0 7,982
Gross unrealized gains 0 0
Gross unrealized losses 0 (9)
Estimated fair value 0 7,973
Municipal bonds    
Debt Securities, Available-for-sale [Line Items]    
Amortized cost 0 2,017
Gross unrealized gains 0 0
Gross unrealized losses 0 (4)
Estimated fair value 0 2,013
Corporate equity securities    
Debt Securities, Available-for-sale [Line Items]    
Amortized cost 4,525 135
Gross unrealized gains 772 1,191
Gross unrealized losses (216) 0
Estimated fair value 5,081 1,326
Warrants    
Equity Securities, FV-NI [Abstract]    
Amortized cost 0 0
Gross unrealized gains 156 0
Gross unrealized losses 0 0
Estimated fair value $ 156 $ 0