GOODWILL AND OTHER INTANGIBLE ASSETS - Changes in Carrying Amount of Goodwill (Details) - USD ($) shares in Thousands, $ in Thousands	1 Months Ended	12 Months Ended
	May 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	May 31, 2019
Goodwill [Roll Forward]
Beginning balance		$ 72,858	$ 72,952
Goodwill, acquired during period		6,179	0
Currency translation adjustments		2	(94)
Ending balance		79,039	72,858	$ 72,952
Business Acquisition [Line Items]
Payments for acquisitions, net of cash acquired		10,934	800	297
Goodwill		$ 72,858	$ 72,858	$ 72,952
In The Chat Communications Inc.
Business Acquisition [Line Items]
Payments for acquisitions, net of cash acquired	$ 10,900
retention based bonus (in shares)	15
Technology | In The Chat Communications Inc.
Business Acquisition [Line Items]
Technology intangible assets					$ 5,100
Goodwill | In The Chat Communications Inc.
Goodwill [Roll Forward]
Ending balance	$ 6,200
Business Acquisition [Line Items]
Goodwill	$ 6,200				$ 6,200