BUSINESS COMBINATIONS - Summary of Fair Value of Consideration Transferred in Acquisition (Details) - USD ($) $ in Thousands		1 Months Ended	8 Months Ended	12 Months Ended
	Apr. 30, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2019
Business Acquisition [Line Items]
Payments for (Proceeds from) Previous Acquisition		$ 8,400
Cloud Savings [Member]
Business Acquisition [Line Items]
Cash and cash equivalents	$ 6,244
Cash			$ 64,363
Financing obligation incurred in connection with acquisition of business	8,604
Contingent consideration liability incurred in connection with acquisition of business	1,600		$ 1,589
Total acquisition price	74,556			$ 74,556
Accounts receivable	5,885
Prepaid expenses and other current assets	804
Property, equipment and software	226
Goodwill	46,515
Other intangible assets	83,841
Accounts payable	693
Accrued merchant and supplier payables	386
Accrued expenses and other current liabilities	6,130
Other non-current liabilities	2,076
Total liabilities assumed	9,285
Other Intangible Assets | Cloud Savings [Member]
Business Acquisition [Line Items]
Intangible assets, useful life				1 year
Intangible assets acquired	687
Trade names | Cloud Savings [Member]
Business Acquisition [Line Items]
Intangible assets, useful life				8 years
Intangible assets acquired	2,609
Developed technology | Cloud Savings [Member]
Business Acquisition [Line Items]
Intangible assets, useful life				2 years
Intangible assets acquired	549
Merchant relationships | Cloud Savings [Member]
Business Acquisition [Line Items]
Intangible assets, useful life				6 years
Intangible assets acquired	$ 20,322