SIGNIFICANT ACCOUNTING POLICIES (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue recognition:
Shipping and handling costs	$ 43,973	$ 40,629	$ 42,619
Cash and cash equivalents:
Maximum original maturity period of temporary cash investments classified as cash equivalents	3 months
Investments:
Marketable securities, maximum maturity period	3 years
Inventories:
Inventories at cost, last-in, first-out (LIFO) method	$ 51,694	53,278
Excess of current cost over LIFO cost of inventories	18,825	17,574
Foreign inventories at cost, first-in, first-out (FIFO) method	$ 4,423	$ 4,253