Marketable Securities (Details 3) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Debt securities, available-for-sale
Less than 12 months, fair value	$ 161,097	$ 264,934
Gross unrealized loss
Less than 12 months, gross unrealized loss	(112)	(64)
US Government bonds and notes
Debt securities, available-for-sale
Less than 12 months, fair value	61,419	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	99,678	250,822
Gross unrealized loss
Less than 12 months, gross unrealized loss	$ (87)	$ (63)