REVENUES (Reconciliation of Deferred Revenue Balances) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
REVENUES [Abstract]
Balance at beginning of period	$ 191,131	$ 198,201	$ 192,783	$ 199,556
Revenue recognized from deferred revenue	(2,079)	(1,905)	(3,731)	(3,260)
Balance at end of period	$ 189,052	$ 196,296	$ 189,052	$ 196,296