ACCOUNTS RECEIVABLE (SIGNIFICANT CLIENTS TABLE) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Concentration Risk, Percentage of Revenue from Major Customer
Accounts receivable, net of allowance of $5,057 and $5,452, respectively	$ 378,397	$ 331,096
Customer Concentration Risk
Concentration Risk, Percentage of Revenue from Major Customer
Concentration risk percentage	10.00%
Revenue | Customer Concentration Risk | Financial Services Client
Concentration Risk, Percentage of Revenue from Major Customer
Concentration risk percentage	13.00%	3.00%	4.00%
Revenue | Customer Concentration Risk | Healthcare client
Concentration Risk, Percentage of Revenue from Major Customer
Concentration risk percentage	6.00%	8.00%	10.00%
Accounts Receivable | Credit Concentration Risk | Financial Services Client
Concentration Risk, Percentage of Revenue from Major Customer
Accounts receivable, net of allowance of $5,057 and $5,452, respectively	$ 58,960	$ 4,321	$ 9,812
Accounts Receivable | Credit Concentration Risk | Healthcare client
Concentration Risk, Percentage of Revenue from Major Customer
Accounts receivable, net of allowance of $5,057 and $5,452, respectively	$ 17,453	$ 18,385	$ 49,245