SEGMENT INFORMATION (Revenues by Service Offering) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenue from External Customer [Line Items]
Revenues	$ 313,525	$ 298,293	$ 283,832	$ 264,482	$ 260,253	$ 236,049	$ 217,781	$ 200,045	$ 1,160,132	$ 914,128	$ 730,027
Software development
Revenue from External Customer [Line Items]
Revenues									841,916	644,732	504,590
Application testing services
Revenue from External Customer [Line Items]
Revenues									223,010	174,259	140,363
Application maintenance and support
Revenue from External Customer [Line Items]
Revenues									74,475	70,551	58,840
Infrastructure services
Revenue from External Customer [Line Items]
Revenues									5,069	11,311	14,198
Licensing
Revenue from External Customer [Line Items]
Revenues									3,141	3,764	3,626
Reimbursable expenses and other revenues
Revenue from External Customer [Line Items]
Revenues									$ 12,521	$ 9,511	$ 8,410