Quarterly report pursuant to Section 13 or 15(d)

Marketable Securities - Continuous Unrealized Loss Position (Details)

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Marketable Securities - Continuous Unrealized Loss Position (Details)
$ in Thousands
Sep. 30, 2018
USD ($)
Investments in an Unrealized Loss Position  
Fair Value $ 1,046,217
Gross Unrealized Losses, less than 12 months (11,555) [1]
Gross Unrealized Losses, 12 months or more 7,300
Corporate debt securities  
Investments in an Unrealized Loss Position  
Fair Value 518,894
Gross Unrealized Losses, less than 12 months (5,866) [1]
U.S. Treasury securities  
Investments in an Unrealized Loss Position  
Fair Value 271,554
Gross Unrealized Losses, less than 12 months (3,291) [1]
U.S. Government agency securities  
Investments in an Unrealized Loss Position  
Fair Value 238,564
Gross Unrealized Losses, less than 12 months (2,251) [1]
Sovereign securities  
Investments in an Unrealized Loss Position  
Fair Value 17,205
Gross Unrealized Losses, less than 12 months $ (147) [1]
[1] As of September 30, 2018, the amount of total gross unrealized losses related to investments that had been in a continuous loss position for 12 months or more was $7.3 million.