REVENUES (Reconciliation of Deferred Revenue Balances) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
REVENUES [Abstract]
Balance at beginning of year	$ 177,962	$ 185,339
Revenue recognized from deferred revenue	(1,669)	(1,342)
Balance at end of period	$ 176,293	$ 183,997