Marketable Securities Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Company's available-for-sales investments
Amortized Cost	$ 18,104	$ 25,635
Gross Unrealized Gains	0	0
Gross Unrealized Losses	13	(28)
Fair Value	18,091	25,607
Corporate notes and bonds [Member]
Company's available-for-sales investments
Amortized Cost	16,603	18,846
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(12)	(25)
Fair Value	16,591	18,821
U.S. government and agency securities [Member]
Company's available-for-sales investments
Amortized Cost	1,501	3,506
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1)	(3)
Fair Value	1,500	3,503
Commercial paper [Member]
Company's available-for-sales investments
Amortized Cost	0	3,283
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	$ 0	$ 3,283