Cash, Cash Equivalents, and Investments (Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Total available for sale securities, Less than 12 months, Fair Value	$ 326,320	$ 133,660
Total available for sale securities Less than 12 months, Gross Unrealized Holding Losses	(1,581)	(82)
Available-for-sale securities, Total Fair Value	326,320	133,660
Available-for-sale securities, Total Gross Unrealized Losses	(1,581)	(82)
Commercial Paper [Member]
Total available for sale securities, Less than 12 months, Fair Value		11,976
Total available for sale securities Less than 12 months, Gross Unrealized Holding Losses		(1)
Available-for-sale securities, Total Fair Value		11,976
Available-for-sale securities, Total Gross Unrealized Losses		(1)
Corporate Debt Securities [Member]
Total available for sale securities, Less than 12 months, Fair Value	326,320	121,684
Total available for sale securities Less than 12 months, Gross Unrealized Holding Losses	(1,581)	(81)
Available-for-sale securities, Total Fair Value	326,320	121,684
Available-for-sale securities, Total Gross Unrealized Losses	$ (1,581)	$ (81)

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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