REVENUES (Reconciliation of Deferred Revenue Balances) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
REVENUES [Abstract]
Balance at beginning of year	$ 185,339	$ 192,783	$ 199,556
Revenue recognized from deferred revenue	(7,377)	(7,444)	(6,773)
Balance at end of year	$ 177,962	$ 185,339	$ 192,783