ACCOUNTS RECEIVABLE (SIGNIFICANT CLIENTS TABLE) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Concentration Risk, Percentage of Revenue from Major Customer
Accounts receivable, net	$ 350,962	$ 391,902
Revenue | Customer Concentration Risk | Healthcare client
Concentration Risk, Percentage of Revenue from Major Customer
Concentration risk percentage	10.00%	7.00%	4.00%
Revenue | Customer Concentration Risk | Telecommunications client
Concentration Risk, Percentage of Revenue from Major Customer
Concentration risk percentage	7.00%	9.00%	10.00%
Accounts Receivable | Credit Concentration Risk | Healthcare client
Concentration Risk, Percentage of Revenue from Major Customer
Accounts receivable, net	$ 49,245	$ 56,802	$ 22,414
Accounts Receivable | Credit Concentration Risk | Telecommunications client
Concentration Risk, Percentage of Revenue from Major Customer
Accounts receivable, net	$ 19,329	$ 27,111	$ 28,080