SIGNIFICANT ACCOUNTING POLICIES (Marketable Securities and Cash Equivalents) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Marketable Securities [Line Items]
Total cash equivalents	$ 8,126	$ 2,048
Short-term marketable securities	52,856	38,179
Total financial assets	60,982	40,227
U.S. Treasury securities
Marketable Securities [Line Items]
Short-term marketable securities	10,133	3,855
Corporate notes and bonds
Marketable Securities [Line Items]
Short-term marketable securities	38,036	32,729
Commercial paper
Marketable Securities [Line Items]
Short-term marketable securities	4,687	1,595
Commercial paper
Marketable Securities [Line Items]
Total cash equivalents	$ 8,126	$ 2,048