SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Summary of Changes in Allowance for Doubtful Accounts) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Changes in allowance for doubtful accounts against accounts receivables:
Balance at the beginning of the period	$ 9,300
Provision for doubtful accounts	6,078	$ 2,710	$ 5,664
Balance at the end of the period	10,700	9,300
Allowance for doubtful accounts
Changes in allowance for doubtful accounts against accounts receivables:
Balance at the beginning of the period	9,300	7,799	4,406
Provision for doubtful accounts	6,078	2,710	5,664
Write-offs	(4,714)	(1,209)	(2,271)
Balance at the end of the period	$ 10,664	$ 9,300	$ 7,799