GOODWILL AND OTHER INTANGIBLE ASSETS - Schedule of Amortizable Intangible Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Goodwill and Other Intangible Assets [Line Items]
Cost	$ 128,218	$ 127,467
Accumulated Amortization	(106,983)	(95,568)
Net Book Value	21,235	31,899
Client-related intangibles
Goodwill and Other Intangible Assets [Line Items]
Cost	63,115	63,164
Accumulated Amortization	(51,224)	(44,835)
Net Book Value	11,891	18,329
Technology
Goodwill and Other Intangible Assets [Line Items]
Cost	59,742	58,942
Accumulated Amortization	(50,398)	(45,372)
Net Book Value	9,344	13,570
Other
Goodwill and Other Intangible Assets [Line Items]
Cost	5,361	5,361
Accumulated Amortization	(5,361)	(5,361)
Net Book Value	$ 0	$ 0
Minimum | Client-related intangibles
Goodwill and Other Intangible Assets [Line Items]
Useful Lives	4 years	4 years
Minimum | Technology
Goodwill and Other Intangible Assets [Line Items]
Useful Lives	3 years	3 years
Minimum | Other
Goodwill and Other Intangible Assets [Line Items]
Useful Lives	1 year
Maximum | Client-related intangibles
Goodwill and Other Intangible Assets [Line Items]
Useful Lives	10 years	10 years
Maximum | Technology
Goodwill and Other Intangible Assets [Line Items]
Useful Lives	10 years	10 years
Maximum | Other
Goodwill and Other Intangible Assets [Line Items]
Useful Lives	5 years