INVENTORIES (Inventories) (Details) - USD ($) $ in Thousands		Dec. 31, 2015	Dec. 31, 2014
INVENTORIES [Abstract]
Finished products	[1]	$ 297,925	$ 275,172
Raw materials		21,765	19,741
Products in process		1,008	1,250
Operating supplies and other		26,375	25,641
Inventories		347,073	321,804
Encumbered inventories		$ 4,452	$ 4,792

[1] Includes inventories encumbered by the purchaser's percentage of volumetric production payments (see Note 1, Deferred Revenue), as follows: December 31, 2015 - $4,452 thousand and December 31, 2014 - $4,792 thousand.