INVENTORIES (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
INVENTORIES [Abstract]
Inventory classified as long-term assets (other noncurrent assets)	$ 11,810	$ 15,285
Inventories valued under the LIFO method	252,808	239,187
Decrease in cost of revenues due to the effect of the LIFO liquidation	2,714	3,956	$ 3,284
Increase in net earnings due to the effect of the LIFO liquidation	1,662	2,419	2,010
Excess of estimated current cost over LIFO cost	168,829	155,576
Approximate effect on net earnings due to the adoption of the LIFO method	$ 8,092	$ (8,338)	$ (7,614)