SIGNIFICANT ACCOUNTING POLICIES - Shipping and Handling Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cost of revenue	$ 14,879	$ 11,170	$ 10,931
Shipping and Handling, Billed
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cost of revenue	513	336	320
Shipping and Handling, Not Billed
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cost of revenue	$ 2,148	$ 1,783	$ 1,502