SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Summary of Changes in Allowance for Doubtful Accounts) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Changes in allowance for doubtful accounts against accounts receivables:
Balance at the beginning of the period	$ 7,900
Provision for doubtful accounts	2,710	$ 5,664	$ 4,030
Balance at the end of the period	9,300	7,900
Allowance for doubtful accounts
Changes in allowance for doubtful accounts against accounts receivables:
Balance at the beginning of the period	7,799	4,406	7,619
Provision for doubtful accounts	2,710	5,664	4,030
Write-offs	(1,209)	(2,271)	(7,243)
Balance at the end of the period	$ 9,300	$ 7,799	$ 4,406