INVENTORIES (Inventories) (Details) - USD ($) $ in Thousands		Dec. 31, 2020	Dec. 31, 2019
INVENTORIES [Abstract]
Finished products	[1]	$ 378,389	$ 391,666
Raw materials		33,780	31,318
Products in process		4,555	5,604
Operating supplies and other		31,861	29,720
Inventories		448,585	458,308
Encumbered inventories		$ 2,416	$ 2,861

[1] Includes inventories encumbered by volumetric production payments (see Note 2), as follows: December 31, 2020 — $2,416 thousand and December 31, 2019 — $2,861 thousand.