SIGNIFICANT CLIENTS(NARRATIVE) (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($) customer	Mar. 31, 2017 USD ($)
Entity Wide Revenue Major Customer Line Items
Revenue	$ 375,249	$ 338,277
Customer Management Services [Member]
Entity Wide Revenue Major Customer Line Items
Revenue	$ 292,641
Customer Concentration Risk | Client A [Member]
Entity Wide Revenue Major Customer Line Items
Number of customers | customer	1
Customer Concentration Risk | Revenue | Client A [Member] | Customer Management Services [Member]
Entity Wide Revenue Major Customer Line Items
Concentration risk percentage	11.30%	2.90%
Minimum | Customer Concentration Risk | Revenue
Entity Wide Revenue Major Customer Line Items
Revenue	$ 100,000