Marketable Securities (Details 3) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale
Less than 12 months, fair value	$ 238,879	$ 264,934
Gross Unrealized Loss
Less than 12 months, gross unrealized loss	(102)	(64)
US Government bonds and notes
Debt Securities, Available-for-sale
Less than 12 months, fair value	134,488	14,112
Gross Unrealized Loss
Less than 12 months, gross unrealized loss	(25)	(1)
Corporate notes, bonds and commercial paper and other
Debt Securities, Available-for-sale
Less than 12 months, fair value	104,391	250,822
Gross Unrealized Loss
Less than 12 months, gross unrealized loss	$ (77)	$ (63)