INVENTORIES (Inventories) (Details) - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016
INVENTORIES [Abstract]
Finished products	[1]	$ 327,711	$ 293,619
Raw materials		27,152	22,648
Products in process		1,827	1,480
Operating supplies and other		27,648	27,869
Total		384,338	345,616
Encumbered inventories		$ 2,808	$ 2,841

[1] Includes inventories encumbered by volumetric production payments (see Note 1, caption Deferred Revenue), as follows: December 31, 2017 - $2,808 thousand and December 31, 2016 - $2,841 thousand.