DEFERRED REVENUE AND COSTS (DEFERRED REVENUE CLASSIFICATION TABLE) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
DEFERRED REVENUE AND COSTS [ABSTRACT]
Deferred revenue - current	$ 39,956	$ 39,447
Deferred revenue - long-term	17,434	23,142
Total deferred revenue	$ 57,390	$ 62,589