Marketable Securities (Details 3) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale
Less than one year, fair value	$ 182,702	$ 264,934
Gross Unrealized Loss
Less than one year, gross unrealized loss	(300)	(64)
US Government bonds and notes
Debt Securities, Available-for-sale
Less than one year, fair value	0	14,112
Gross Unrealized Loss
Less than one year, gross unrealized loss	0	(1)
Corporate notes, bonds and commercial paper and other
Debt Securities, Available-for-sale
Less than one year, fair value	182,702	250,822
Gross Unrealized Loss
Less than one year, gross unrealized loss	$ (300)	$ (63)