REVENUES - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Disaggregation of Revenue [Line Items]
Revenues	$ 1,671,952	$ 935,152	$ 3,575,550	$ 1,818,190
Americas
Disaggregation of Revenue [Line Items]
Revenues	1,428,061	715,919	3,032,533	1,394,341
Europe
Disaggregation of Revenue [Line Items]
Revenues	207,723	160,349	452,085	303,218
Asia Pacific
Disaggregation of Revenue [Line Items]
Revenues	36,168	58,884	90,932	120,631
Operating Segments | Merchant Solutions
Disaggregation of Revenue [Line Items]
Revenues	1,001,555	929,914	2,216,824	1,807,696
Operating Segments | Merchant Solutions | Relationship-led
Disaggregation of Revenue [Line Items]
Revenues	566,414	502,239	1,242,935	961,281
Operating Segments | Merchant Solutions | Technology-enabled
Disaggregation of Revenue [Line Items]
Revenues	435,141	427,675	973,889	846,415
Operating Segments | Merchant Solutions | Americas
Disaggregation of Revenue [Line Items]
Revenues	862,927	715,919	1,887,433	1,394,341
Operating Segments | Merchant Solutions | Europe
Disaggregation of Revenue [Line Items]
Revenues	102,460	155,111	238,459	292,724
Operating Segments | Merchant Solutions | Asia Pacific
Disaggregation of Revenue [Line Items]
Revenues	36,168	58,884	90,932	120,631
Operating Segments | Issuer Solutions
Disaggregation of Revenue [Line Items]
Revenues	470,025	5,238	973,787	10,494
Operating Segments | Issuer Solutions | Americas
Disaggregation of Revenue [Line Items]
Revenues	363,140	0	756,893	0
Operating Segments | Issuer Solutions | Europe
Disaggregation of Revenue [Line Items]
Revenues	105,263	5,238	213,626	10,494
Operating Segments | Issuer Solutions | Asia Pacific
Disaggregation of Revenue [Line Items]
Revenues	1,622	0	3,268	0
Operating Segments | Business and Consumer Solutions
Disaggregation of Revenue [Line Items]
Revenues	216,722	0	420,668	0
Operating Segments | Business and Consumer Solutions | Americas
Disaggregation of Revenue [Line Items]
Revenues	216,722	0	420,668	0
Operating Segments | Business and Consumer Solutions | Europe
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Operating Segments | Business and Consumer Solutions | Asia Pacific
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Revenues	(16,350)	0	(35,729)	0
Intersegment Eliminations | Americas
Disaggregation of Revenue [Line Items]
Revenues	(14,728)	0	(32,461)	0
Intersegment Eliminations | Europe
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Intersegment Eliminations | Asia Pacific
Disaggregation of Revenue [Line Items]
Revenues	$ (1,622)	$ 0	$ (3,268)	$ 0