GOODWILL AND OTHER INTANGIBLE ASSETS - Schedule of Amortizable Intangible Assets (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Goodwill and Other Intangible Assets [Line Items]
Cost	$ 128,239	$ 128,218
Accumulated Amortization	(109,930)	(106,983)
Net Book Value	18,309	21,235
Client-related intangibles
Goodwill and Other Intangible Assets [Line Items]
Cost	63,136	63,115
Accumulated Amortization	(52,839)	(51,224)
Net Book Value	$ 10,297	$ 11,891
Client-related intangibles | Minimum
Goodwill and Other Intangible Assets [Line Items]
Useful Lives	4 years	4 years
Client-related intangibles | Maximum
Goodwill and Other Intangible Assets [Line Items]
Useful Lives	10 years	10 years
Technology
Goodwill and Other Intangible Assets [Line Items]
Cost	$ 59,742	$ 59,742
Accumulated Amortization	(51,730)	(50,398)
Net Book Value	$ 8,012	$ 9,344
Technology | Minimum
Goodwill and Other Intangible Assets [Line Items]
Useful Lives	2 years	2 years
Technology | Maximum
Goodwill and Other Intangible Assets [Line Items]
Useful Lives	10 years	10 years
Other
Goodwill and Other Intangible Assets [Line Items]
Cost	$ 5,361	$ 5,361
Accumulated Amortization	$ (5,361)	$ (5,361)
Other | Minimum
Goodwill and Other Intangible Assets [Line Items]
Useful Lives	1 year	1 year
Other | Maximum
Goodwill and Other Intangible Assets [Line Items]
Useful Lives	5 years	5 years