Quarterly report pursuant to Section 13 or 15(d)

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

v3.19.3
Basis of Presentation and Summary of Significant Accounting Policies - Investment Categories (Details) - USD ($)
$ in Thousands
Sep. 30, 2019
Dec. 31, 2018
Equity Securities, FV-NI [Abstract]    
Estimated fair value $ 8,314 $ 9,257
Debt and Equity Securities, FV-NI [Abstract]    
Amortized cost 876,074 600,154
Gross unrealized gains 1,010 1,226
Gross unrealized losses (2,701) (163)
Estimated fair value 874,383 601,217
Bank deposits    
Debt Securities, Available-for-sale [Line Items]    
Amortized cost 490,828 311,066
Gross unrealized gains 294 26
Gross unrealized losses (11) (29)
Estimated fair value 491,111 311,063
Corporate bonds    
Debt Securities, Available-for-sale [Line Items]    
Amortized cost 58,581 53,223
Gross unrealized gains 240 1
Gross unrealized losses 0 (45)
Estimated fair value 58,821 53,179
Commercial paper    
Debt Securities, Available-for-sale [Line Items]    
Amortized cost 322,160 225,731
Gross unrealized gains 86 8
Gross unrealized losses (29) (76)
Estimated fair value 322,217 225,663
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 4,505 135
Gross unrealized gains 325 1,191
Gross unrealized losses (2,661) 0
Estimated fair value 2,169 1,326
Warrants    
Equity Securities, FV-NI [Abstract]    
Amortized cost 0 0
Gross unrealized gains 65 0
Gross unrealized losses 0 0
Estimated fair value $ 65 $ 0