SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details 5) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2016	Dec. 31, 2015
Accounting Policies [Abstract]
Proceeds collected through a surcharge on certain customers' bills	$ 500
Cash and cash equivalents	94,776	$ 47,176
Restricted cash (included in taxes, prepaid expenses and other assets)	524	539
Total cash, cash equivalents, and restricted cash shown in the statements of cash flows	$ 95,300	$ 47,715	$ 25,935	$ 9,346