GOODWILL AND OTHER INTANGIBLE ASSETS - Schedule of Amortizable Intangible Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Goodwill and Other Intangible Assets [Line Items]
Cost	$ 133,344	$ 128,218
Accumulated Amortization	(113,627)	(106,983)
Net Book Value	19,717	21,235
Client-related
Goodwill and Other Intangible Assets [Line Items]
Cost	63,140	63,115
Accumulated Amortization	(54,368)	(51,224)
Net Book Value	8,772	11,891
Technology
Goodwill and Other Intangible Assets [Line Items]
Cost	64,843	59,742
Accumulated Amortization	(53,898)	(50,398)
Net Book Value	10,945	9,344
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
Goodwill and Other Intangible Assets [Line Items]
Useful Lives	4 years	4 years
Minimum | Technology
Goodwill and Other Intangible Assets [Line Items]
Useful Lives	2 years	2 years
Minimum | Other
Goodwill and Other Intangible Assets [Line Items]
Useful Lives	1 year	1 year
Maximum | Client-related
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	5 years