SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Reconciliation of Deferred Revenue Balances) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES [Abstract]
Balance at beginning of period	$ 206,468	$ 214,060	$ 219,968
Amortization of deferred revenue	(6,912)	(7,592)	(5,908)
Balance at end of period	$ 199,556	$ 206,468	$ 214,060