REVENUES - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Disaggregation of Revenue [Line Items]
Revenues	$ 1,903,598	$ 883,039
Americas
Disaggregation of Revenue [Line Items]
Revenues	1,604,471	678,423
Europe
Disaggregation of Revenue [Line Items]
Revenues	244,361	142,869
Asia Pacific
Disaggregation of Revenue [Line Items]
Revenues	54,766	61,747
Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	1,922,977	883,039
Operating Segments | Merchant Solutions
Disaggregation of Revenue [Line Items]
Revenues	1,215,269	877,783
Operating Segments | Merchant Solutions | Relationship-led
Disaggregation of Revenue [Line Items]
Revenues	676,522	462,387
Operating Segments | Merchant Solutions | Technology-enabled
Disaggregation of Revenue [Line Items]
Revenues	538,747	415,396
Operating Segments | Merchant Solutions | Americas
Disaggregation of Revenue [Line Items]
Revenues	1,024,504	678,423
Operating Segments | Merchant Solutions | Europe
Disaggregation of Revenue [Line Items]
Revenues	135,999	137,613
Operating Segments | Merchant Solutions | Asia Pacific
Disaggregation of Revenue [Line Items]
Revenues	54,766	61,747
Operating Segments | Issuer Solutions
Disaggregation of Revenue [Line Items]
Revenues	503,762	5,256
Operating Segments | Issuer Solutions | Americas
Disaggregation of Revenue [Line Items]
Revenues	393,754	0
Operating Segments | Issuer Solutions | Europe
Disaggregation of Revenue [Line Items]
Revenues	108,362	5,256
Operating Segments | Issuer Solutions | Asia Pacific
Disaggregation of Revenue [Line Items]
Revenues	1,646	0
Operating Segments | Business and Consumer Solutions
Disaggregation of Revenue [Line Items]
Revenues	203,946	0
Operating Segments | Business and Consumer Solutions | Americas
Disaggregation of Revenue [Line Items]
Revenues	203,946	0
Operating Segments | Business and Consumer Solutions | Europe
Disaggregation of Revenue [Line Items]
Revenues	0	0
Operating Segments | Business and Consumer Solutions | Asia Pacific
Disaggregation of Revenue [Line Items]
Revenues	0	0
Intersegment Revenue
Disaggregation of Revenue [Line Items]
Revenues	(19,379)	0
Intersegment Revenue | Americas
Disaggregation of Revenue [Line Items]
Revenues	(17,733)	0
Intersegment Revenue | Europe
Disaggregation of Revenue [Line Items]
Revenues	0	0
Intersegment Revenue | Asia Pacific
Disaggregation of Revenue [Line Items]
Revenues	$ (1,646)	$ 0